PPC Accident on Takeoff

[Bruce Brown]

This has been copied from a post on the Yahoo list...

I usually don't bother Y'all on this list, but this is important information that may save someone in the future. I would like to share with you what happened to me during my takeoff last Sunday morning. We often hear about pilot error on takeoff causing a roll over or other accident, but rarely, if ever is it determined to be caused by a failed component of the craft. This is one of those rare times, and it took me completely by surprise.

There was a light east wind and I was setup to takeoff directly into it. The grass was a little tall for my field, but not compared to many that I have flown from, and it was wet with dew. Temp was probably in the mid 60's. Conditions were pretty good. I did have a 90 pound load in the back seat as this was a trial run in preparation for a couple of day cross country flight that I had planned for this weekend. Just for the record, I have flown with a 317 pound passenger before without any trouble at all and still had a 400 fpm climb rate.

This takeoff was no different than many before it, at first anyway. I held my brake and pushed the throttle wide open. When the front wheel began to slide I released the brake and the cart rolled forward pulling the chute up into the air. The roll out was slow and the chute didn't want to go up, but instead began a side to side number that they are famous for when not loaded. I caught the chute on it's way up and pushed out on the flare with the engine still at full throttle to get the cart up to speed and load the chute. As in the past when using this technique to tame the chute it stopped rocking and the cart leaped off of the ground. At this point I am at full throttle and about 3/4 flare, and at about 10' agl the nose begins to roll forward from the 45 degrees or so that it was. I pushed out the rest of the flare and kept the throttle open, but the nose just kept going over and plowed into the earth.

The nose wheel planted itself in the dirt and the chute assisted by the prop at full power, pole vaulted the machine using it as a pivot point. It hit the ground hard, upside down and moving backwards. The whole thing from the moment I first lifted off until it was over was about 3 seconds. I was stunned, but not seriously hurt. I got 2 small bumps on my shins and a bruised bone near the wrist. When the machine impacted the ground the prop sounded like a cannon going off as it exploded and left just three short stubs with the metal adjusters exposed. The goggles were ripped from my head as the machine and I slid across the field and my leather helmet is a bit scuffed up, but it protected me from any cuts or scrapes on the head. The airframe is basically trash now, but it did a wonderful job of protecting me in this catastrophic event. I built this machine myself last winter and it was made of welded steel tubing. The tubes got bent and deformed, but not a single weld cracked. Looking at the tubing and how it is bent and scraped up tells the story of how much protection I got from it. After this I am very much more a believer in the welded steel frames, frontal bars, overhead bars, etc. All of them together played a part in my walking away from this accident.

For a few days I could not figure out exactly what went wrong and tried to just write it off as pilot error, but I couldn't. Even if it was pilot error I needed to know why it happened so I would not ever do it again. In getting some help from my friends and discussing what happened with them we came up with various reasons for such an occurrence other than some freaky unseen wind or something. We figured that something must have happened to the power during the takeoff, but the engine sounded great and it was at full throttle all the way. I should have just climbed like a bat once the cart left the ground. Marty plugged in the numbers from my prop into a program that he has and it came up with a warning that using the exact combination of engine/ gear ratio/ prop that I had was in a stall until the cart reached a forward speed of 29 mph! All of a sudden it all made perfect sense and the pieces of the puzzle fit.

With the prop stalled and not producing good thrust, and the extra weight and wet grass, the cart speed was slow. I forced the plane to lift by flaring and that changed the air pressure between the chute and prop causing ground effect and the prop faltered even more in the stall, or stalled more and it was just like loosing power 10' after leaving the ground. But it was worse since the engine was still running wide open and there was thrust being produced, it just wasn't enough to fly the plane and under a parachute that is not a good thing. The pendulum effect took over and the nose went over, then the prop thrust just drove it to the ground. From 10' there is no time to do anything, and I don't know what else I could have done at that point anyway, except maybe kill the engine to save the prop, but it happened too fast. All I could do was get as much flare applied as there was available and ride it out.

I will share the blame on this accident because I did not abort when the chute was going side to side, but I routinely do what I did to get the rocking chute under control and get into the air. It's just one of those things that some of us sometimes have to do with an elliptical chute. That is not what caused this however, it was the stalled prop on the takeoff that caused it. I had been using a 68" Medium Ivo prop, and it is a very high pitch prop. It was fantastic as a cruising prop and I averaged a 2.4 gph fuel burn with it on cross country flights. That is what I was after when I bought the prop and I was as happy as could be to have it. I never knew anything about it being in a stall zone until it reached 29 mph though. I never even considered such a thing as I had never heard of it happening before.

I felt compelled to share this with you in case it might save someone else from making the same mistake that I did in running this prop on a PPC. On a fixed wing it would be a super prop at the higher speeds, but on a ppc it is DANGEROUS! It stalls out right when we need it most, during takeoff up to 29 mph. I would think that it might even be worse on a square wing that only flies at 26-30 mph than it was with my elliptical that flew at 33 mph
+. I built and redesigned my own machine and I have no one to blame for
+the
combination that I used but myself, but boy did I ever learn a lesson about props and the value of high static thrust! :)

The Renegade will rise from the ashes like a Phoenix! I already had a crate of chromoly in the barn and I can use everything from the wreck except the welded steel components and prop and strobe light. They were destroyed beyond repair, or reasonable repair anyway. I'm rebuilding the Renegade out of 4130 and replacing the 68" Medium Ivo prop with a 72" 4 blade Warpdrive prop. That is my project for next the next month or two. :) In the meantime I will be picking up my new Model A from Airframes Unlimited next week and will be back in the air.


Have a good one!

Steve

Heartland Airframes Unlimited
Dexter, KY

Authorized Factory Representative for Airframes Unlimited www.airframesunlimited.com

American Spirit website; www.americanspiritppc.com
E-mail steve@americanspiritppc.com

[camp willys]

Im gunna be taking lessons and purchaseing a ppc this spring. I am glad you shared your accident as they help myself and other beginers realize that it can be danerous and to progress slowly with big ears. thank you.

[Rich K]

Bruce,

Thanks for passing that along.


One thing which bothered me a bit was the writers take off procedure.
Darn if it didn't sound like an aircraft carrier take off procedure.

For me -- flaring on/for take off was never a consideration.
Further, I never use full power until my canopy is steady and overhead which is one of the recommended procedures to avoid rollovers, even though that was not a consequence of the writers experience.

Simply, if I don't have the room for a safe take off without the need to flare I'm in the wrong field !!

I'm pleased the writer survived the incident and took the opportunity to educate us all.


Rich K

[ByrdMan]

He mentions that it is an eliptical. I have never flown one but have a Chiron video and have read a couple of articles that talk about using flare on takeoff to keep the wing from overrunning the cart.

[larsenwv]

I have a couple of questions about this. What especially puzzles me is how the prop can stall and, especially, what the airspeed of the cart has to do with a prop stalling. I know that the prop is an airfoil. But I can't think how the scenario described above changed the angle of attack of the prop and made it stall. And what does the speed to the cart have to do with the angle of attack of the prop? It would seem to me that the relevant speed for a prop would be RPMs. No doubt I am missing something important. The explanation sounds really well thought out and it is certainly a pertinant warning for PPC pilots (except that most of us fly factory designed machines with standard props, presumably without this design flaw). Anyway, can someone explain the dynamics of propeller stall and the relevance of cart speed to propellor stall? I'm a little unclear, too, about how the cart was moving relative to the chute. From what I can make out, the wing got ahead of the cart, at which point, pendulum took over and the cart went down toward the ground. But in the account, it says the pilot was moving backwards. How did that happen? It seems like once the nose hit, if the chute was out ahead, the tail would be pulled over the top and one would be moving forward the whole time.

[mignazito]

Actually props can and sometimes do stall. Stall as you should all know is when the AOA exceeds the critical angle. A props AOA is NOT it's pitch. The AOA of a prop is it's pitch reduced by the "advance ratio" which is deteremined by the prop rpm and it's forward speed. Basically higher flight speed less AOA at a given pitch. At static the prop AOA is highest. In some cases a prop can have a high enough pitch to be stalled at static. Unlike a wing a stalled prop still produces thrust but at lower efficiency. Well it really is the same, but the prop does not quit working just because it is in stall. If you have a prop in stall at static, as you gain forward speed the AOA decreases and the prop will "break out" of stall at some certain speed. If this speed is well below takeoff speed in a PPC, there is no problem.

I am familiar with the situation with Steve's prop. That prop "broke out" of stall right at or near takeoff speed when at full power. This is an unstable operating point on the prop curve where it "wavers" in and out of stall produce a widely flutuating level of thrust. Just what you do not want in a PPC right at liftoff. Steve can attest to what might happen. That prop was not replaced as is, but a better selection was used. BTW I told Steve this would happen before he used that prop.

For PPCs it is best not to have prop stall at any operating condition as the "break out" can be a problem even in the kiteup run. If it is in stall at static and if it breaks out at very low speed like 4 or 5 mph it will be acceptable. Sometimes an efficient prop selection will do just that.

Hope that helps you understand this incident.

Elliptical chutes require more of a full power kiteup than square wings BTW.

Marty

[JGatto]

I’m not disagreeing with Steve and Marty’s analysis, but I’ve experienced a metastable stall with my elliptical rig on takeoff that sounds very similar to the circumstances surrounding Steve’s accident.

The chute looked good, I kept the coal on, and I lifted off to about 10 ft – then it got mushy and I started a descent . . . at full power. The chute had actually “locked-out” at a very high angle over the cart before I left the ground. I had enough lift and thrust to get off the ground, but not enough to keep altitude. Before I touched back down, the cart swung under the chute and bing – the stall was corrected and I could fly normally.

This “high angle lockout” situation is still difficult for me to judge visually – which means I now pay special attention to my acceleration and velocity during every takeoff run. If the wing is clean and flying, I'll zip along smoothly; if the wing is hanging back a bit, I'll feel it drag.

- John

[Gary Fisher]

A few others have experienced the metastable wing stalls, typically when applying full throttle and flare at the same time, and sometimes when hitting turbulence in the process. Unfortunately, the pilot usually keeps up full throttle to fight the descent, but this only locks it place. If the cart is allowed to swing back under the chute, it may resume flying, then throttle can be re-applied.

A fast elliptical is less likely to experience this, and the flare-on-takeoff technique is used to avoid having the wing slingshot past (in front of) the cart. If high power is used, the flare is not needed (as I thing Marty will confirm). The overflight of the wing only happens when power is reduced too much as the wing is coming overhead. This slows the cart down as the momentum keeps the wing shooting forward.

[Dennis Bowers]

Actually props can and sometimes do stall. Stall as you should all know is when the AOA exceeds the critical angle. A props AOA is NOT it's pitch. The AOA of a prop is it's pitch reduced by the "advance ratio" which is deteremined by the prop rpm and it's forward speed. Basically higher flight speed less AOA at a given pitch. At static the prop AOA is highest. In some cases a prop can have a high enough pitch to be stalled at static. Unlike a wing a stalled prop still produces thrust but at lower efficiency. Well it really is the same, but the prop does not quit working just because it is in stall. If you have a prop in stall at static, as you gain forward speed the AOA decreases and the prop will "break out" of stall at some certain speed. If this speed is well below takeoff speed in a PPC, there is no problem.
.

.

Marty
Dang, why did'nt I think of that!

[George Fogleman]

Could this have been worse had the wing been a square instead of an elliptical ? I ,for one, enjoy flying "slow and low". With my square, I take off using 3/4 power , back off and check chute, then go to full power . I am heavy and enjoy my 550 ... plenty of lift... Since it does fly slower, I reach take-off speed sooner than some, and still have plenty of field in front of me. Some may disagree with me, but I feel that a square wing and a PPC belong together. I have heard too many things about an elliptical ....higher take off speeds ... way too many aborts to suit me ...etc. There are benefits also, so I can "stand corrected". Just "Square Me"....George Fogleman

[mignazito]

In the final analysis we must all decide what is right for each of us. Of course that does not mean what we like or want will suit others. We can however have disucssions that point out the pros and cons of various options in a clear, concise unbiased way so that each of us can decide what will suit us. There are often many anecdotes about what has been observed. I try not to doubt some ones observations. They ussually saw what they saw and there is little arguement about that. What we can examine are he conclusions drawn from those observations.

I have had as much or more experience with ellipticals than most anyone in the PPC industry. I have sold close to 70 of them and either rigged them personally or advised the owner on proper rigging. I have corrected rigging problems on many of my competitors wings as well as some of ours that have been bought second hand and rigged by owners. After seeing most of the major reported problems being eliminated or greatly reduced by proper rigging, it is my carefully considered opinion that improper rigging is the source of the majority of reported observations of elliptical problems.

I invite you to come here any time and fly my Buckeye 582 DM with any one of my three ellips (E280, E310 and E340). They all kite up smooth and straight with no problems EVERY TIME and with no heroic pilot input required. No dancing on the footbars, no diddling around, no swing and sway, no holding your mouth the right way, NOTHING special other than a little smooth piloting. All due to a carefully refined rigging setup I have come to over time and hands on experience that will work on any PPC.

Ellpiticals may not be for you for a variety of reasons that suit you personally. Those reasons may not suit everyone however and there are benefits to be had. If you have the least curiousity as to what those benefits might be, come on over to my place and let me show you.

Marty

[jyonkin]

This sounds much more like a depature stall that was the result of pilot error. One of the problems created by elliptical wings is the need for high power and the tendancy for the transition from ground to flight happening in quick fashion. When I first read this account when it was posted in 2003 I felt the same thing. Pilot error.

J Yonkin

[mignazito]

John:

Sorry to disappoint you, but not so in this case. The offending prop was replaced (it was destroyed in the incident) and this problem NEVER occured again for this pilot still flying elliptical wings to this day. In addition Steve is highly experienced with ellipticals and had not had this problem before or has he had it since after replacing the offending highly over pitched prop.

Sure other things can happen under other circumstances, but this particular incident is pretty clearly due to a prop that operates in stall well into flying speed at WOT. Though not seen often, it is possible so one should beware of using a very slow turning prop which because of a lack of enough blade area requires a very high pitch. That is the lesson that should not be overlooked in this incident.

Yes you can bolix up an elliptical launch. I personally have not had such an incident occur or even begin to occur though I am ready to abort at the first sign of trouble. Could just be dumb luck on my part after well over 100 hours of elliptical flight and some 500 hours of total time. I like to maintain full or near full power all throughout my launch. With the rigging setup I have that eliminates most classic elliptical problems, launches invariably are pretty much non events. Smooth straight kiteup to overhead where I ease off power slightly to lengthen the run a bit for a visual looksee, then WOT for liftoff.

Baubling the wing by reducing too much power during the critical parts of the kiteup can lead to trouble at liftoff, but luckily (or due to skill?) I have so far not had this problem.

Trust me, with that prop Steve had the best elliptical pilot in all of PPC land would have had trouble. In fact Steve is one of the best and had trouble. That was one really BAD prop selection. What out for such a situation if some one trys to sell you a prop match like that one. A 3.47:1 drive with only 3 - 68" blades. Bad news.

Marty

[Joe Hines]

Marty,
First, thanks for the articles and insight. I too have been flying elliptical chutes for quite a while. I have over 450 hours on a Chiron (the seventh chute they imported into North America in fact). I have had a hard time explaining that the elliptical myths are just that, myths. Your work and words make that much easier for me, thanks again.
Your rigging article explains a lot. I built my own PPC years ago, and rigged it as described in your article. No, I do not claim to have discovered that as the best way to rig the chute, just dumb luck. It does work though. In the hundreds of take-off I have made flying the Chiron, the only incidents, (one roll over, 4 or 5 aborted take-offs), were entirely caused by me, with one glaring exception. I had either left the trim adjusters too tight, or in the case of roll over, simply set up in a cross wind.
The exception was when I put a R&D tuned pipe on my 503. It sure made some HP, but I couldn’t get the prop pitched to use it. I had the prop stall on at least two occasions, although I didn’t know it at the time. After reading your post I am pretty sure that was the reason for the loss of thrust. Anyway the pipe is hanging on a nail in the shop, where it can’t outsmart me again.

[mignazito]

Joe:

Thanks for your note. Over time I have come to the same realization that you have come to independently. Though some added skill is required to handle an elliptical, far and away most of the alleged problems are due to rigging errors. This is pretty much independent of mfg too though support after the sale is a major issue. That is often a point of sale issue. Some of these rigging anomolies are pretty small nuances. But if you get everything just right, the vast majority of the alleged "built in" problems with ellips miraculously disappear. They are exquisitely sensitive to anything that is the least bit "off" while the common square is insensitive to most anything including control inputs.

Keep flying that ellip safely and enjoy it. They are great. I won't ever buy another square. I'd maybe take one for free, but not put out money for one.

Marty

[ByrdMan]

Marty or Joe,

Could you tell me where I could get a copy of the Marty's rigging article on setting up an elliptical Joe referenced?

Thanks,

[mignazito]

Joel:

Send your e-mail address to me at mdipe@consoldiated.net and I will send you a copy in Microsoft Works format. You can open this file in Microsoft Word too. it is complete with all pictures.

It was in the February issue of Aero Connections Magazine and you might be able to et a copy from Aero Sports Connection as well.

Marty

[jyonkin]

Marty: I still disagree. Why don't we hear of prop stalls during climb in flight? Why not other reports of stalls with the "offending prop". BTW I should be clear that I do understand that props can stall. I just don't feel that it was the contributing factor in this incident. The pilot failed to have the wing overhead before transition occured, the crash was happening before he left the ground and the wing stalled. Findings: Pilot's failure to properly configure the vehicle for flight resulting in a departure stall and uncontrolled flight into terrain.

J Yonkin

[mignazito]

Honest men can have honest disagreements. I'll try one more time and then I'll give up since you seem quite persistent and I don't have that much time left in my life to convince you.

You do not see prop stalls very often because it is such a bad prop selection that no one who knows what they are doing uses it. That is not to say it could'nt slip into some one's application as it did in Steve's case. Now Steve knows better. That question is irrelevent..

Secondly prop stall once in flight is NOT a real problem since all that results is inefficient thrust production once the stall is established. You can fly along FD&H all day long with a prop frimly in stall. The BIG problem is when a prop is at the verge of stall right at takeoff where it wavers in it's output like in Steve's case. Here it can have severe effects as Steve can attest to.

As I said before there are other conditions that can cause somewhat similar problems with an ellip at takeoff, but that is NOT what happened in Steve's case.

If you insist on disagreeing, I have no problem with that. You will have to prove your suppositions to the rest of the forum as I have said about all I plan to say on this issue.

As I said, honest men can have honest diffrences of opinion and still be friends. As a friend however I do caution you that very steeply pitched props applied to a PPC should be analysed by some one who knows what they are doing to see if there is a potential stall breakout problem.

Marty

[jyonkin]

Marty: I should have been a bit clearer. I agree that the prop may have stalled is this case. I disagree that the stall alone caused the crash. The pilot's actions (WOT 3/4 flare) created a situation where the wing was able to transition to flight while being behind the cart.(not unlike a departure stall) Thus my point for saying the "vehicle" was not configured properly.

From some research I was able to do it appears that having a propeller stall at WOT and at "flying speed" is not typical. Is this your opinion?

It also looks like you may have informed the pilot that this could occur. Are there other combinations of prop size and number that we should be wary of out there?

J Yonkin

[mignazito]

John:

Certainly other factors can make a prop stall more "ugly" than it can be otherwise. The wing Steve had was and still is often used with the takeoff technique Steve described by many pilots. In spite of your suspicions, I have to tell you it was not a major factor since he flew the same wing afterwards with a different prop and no problems and no problems using the same takeoff technique either. I myself have flown this same wing using the same technique so I do not concur that your analysis is relevant. Certainly not in this case. It turns out if you rig it right this technique is not needed, but many still use it for this wing with no problems or few anyway. Nothing like what happened to Steve at any rate.

Prop mechanics is not well understood by many. In fact my delving into this realm was prompted by my frustration with trying to get information from the industry about props including the prop mfgs themselves. Funny how some folks can make something they really know little about. Getting to the right "geek" in the back room is the main problem. I have talked to Ivo at some length and he knows what's up, but getting to him is not always possible. I know the fan laws well from my experience in HVAC work and the answers I was getting made no sense. Mainly a lot of mumbo jumbo. I proceeded to wade thru all the NASA/NACA papers on props and a few books on the subject. Along the way I acquired a computer program that not only predicts prop performance with great accuracy, but tells you when it is in, approaching, on the verge and out of stall. A very handy thing to know.

Are prop stalls a widespread issue to be concerned about? Yes and no. Some big engines using props without enough blade area should be evaluated as these will have very steep pitches that lead to the prop stall problem particularly at WOT. Otherwise this problem is relatively rare though I have seen some I would be wary of. Clues? Low prop rpm (high ratios like 3.47:1 or greater and/or low rpm engines) with small diameter and low blade numbers (low blade area). These setups will have very steep pitches like 16 degrees or more at the 75% station (another clue) on a PPC.

Can you have some stalled operation and still be alright? In fact a very efficient prop selection even on a PPC will sometimes have some stall at static and maybe up to about 10 mph of airspeed. It then "breaks out" and will not cause problems though sometimes on low powered rigs it can lead to "lockouts" at partial kiteup. You can ussually make a selection about as good and avoid stall throughout the operating range. That is the method I prefer and use in my prop selections. It just leaves less room for problems. I have done hundreds of these for owners as well as mfgs.

It should be made clear that prop stall though technically like wing stall does not give any clear signals other than some noise or sound change that might be noticed (or might not). It simply abruptly reduces the prop efficiency as it transitions into stall and similarly abruptly regains effiency as it "breaks out". Since we do not have control issues like we have with stalled wings, the phenomenon is more or less invisible to the pilot.

High speed fixed pitch prop airplanes quite often have deeply stalled props at static and sometimes are still stalled well past takeoff speed. This is not an issue as long as the transition is done well after takeoff when the nose is lowered to accellerate to cruising speed and the airplane has some altitude. Once in cruise the prop is well out of stall and at the right pitch for the higher operating speed. A necessary compromise for a fixed pitch prop on a fast airplane.

Such a setup on a PPC is a recipe for disaster however. If the prop is transitioning in or out of stall or worse yet wavering in and out say due to shifting winds at critical kiteup or right at liftoff, nasty things can happen as Steve can tell you.

I urge you to stop trying to write this incident off to factors other than a very bad prop selection. It was certainly the case with this one. Though not often seen, it is a posibility and your prop selection should be reviewed if you see any of the clues I mentioned above.

Please understand, I am not trying to impose my will in this discussion. My intentions are to help pilots avoid what could be a very nasty situation that most are unaware can even exist. I sometimes get frustrated when some one rebels at this or another not well understood concept and puts up a persistent and protracted "fight" to resist the immutable laws of physics behind it. I'm working hard to keep my cool and be of some use to everyone since I think the discussion here is well intentioned and open.

Marty

[mignazito]

John:

Though prop stalling is realtively uncommon, it is often right under our noses. Here is one seen all too often:

100 hp 912ULS with 62" - 3 bladed prop.
Pitch at 75% station 20 degrees!!!!!!

This prop is in stall at WOT ALL THE TIME FROM STATIC UP TO CRUISE. In fact it remains in stall even when backed down to cruise power and does no break out till well below cruise rpm. When in glide essentially.

This is a pretty odd situation and since it never breaks out except on final approach, probably would not give much trouble. The only real "nasty" I could envision would be if power was applied due to some need close to the ground on final where there could be an issue arise.

The biggest problem with this selection is lousy prop efficiency. Since the motor is so grossly overpowered this goes unnoticed to the uninitiated or unaware. What this engine needs is at least a 5 blade at 68" or larger where not only is there no stalled operating point at any speed or rpm, but it makes a ton more thrust. I have such a rig here with a 68" - 5 making 520 lbs static on a sealevel day. A real slap in the back.

Marty

[jyonkin]

Marty: Thanks for the additional info on potential configurations that may lead to problems. (prop stall) This information has not been widely discussed and I agree that it is not understood by many in the PPC marketplace.

I still consider the accident a result of pilot error. Let's agree that the prop was stalling during the take off role (WOT as stated) The pilot even noted that he had a slower ground role than normal. He attributes this to wet grass but it was likely the prop stalling. He takes actions to get the wing under control and by using flare (3/4 brakes) creates enough lift to get the vehicle 10' in the air where (the prop still in stall) it comes back to earth (uncontrolled flight into terrain) The pilot failed to recognize the situation and take appropriate action. Instead the pilot did what he "always did" because of his experience.

Cause of accident: Uncontrolled flight into terrain.
Contributing factor: (1) Propeller stall resulting in reduced ground speed on take off roll. (2) Pilot's failure to analyze the situation and take appropriate action. (3) Pilot's failure to follow recommendations of Marty.

Once again thanks for the stall info...very interesting and good to know.

J Yonkin

[mignazito]

John:

I still don't think you are getting this prop stall situation quite right in your mind. If the prop is already in stall and remains in stall it simply is not a problem at all. You have the thrust you have and that's that. This prop was in stall at static and as as long as it remained in stall everything was fine. The PPC responded to pilot inputs just fine. The problem is in the "break out" or transition from stalled to unstalled. Here the propeller output becomes very erratic and no amount of pilot input will help PERIOD end of discussion. If this breakout occurs at a low speed well below takeoff speed in a PPC, there is generally no probelm though it could have a negative effect on kiteup. The real danger and what happended to Steve is that breakout and erratic thrust output coincided with liftoff speed. A surging prop thrust at this point plays hob with a PPC. There was really no effective pilot input once it lifted off with this problem.

You simply have to stop clinging to this notion of pilot error in flight in this case. Simply not so. Deciding to use this prop against my advise might be construed as poor judgement, but only if you trust me. Steve now implicitely does trust me BTW.

You have it fundementally wrong. Short of aborting before takeoff, there was nothing Steve could have done. Perhaps failure to abort might concievably qualify as a pilot error, but the circumstances were unussual and I myself even knowing what I know might have made the same error in pressing on. The flare on takeoff is NOT an unussual manuever for the wing he had nor is it an error. This is not the ussual square ragbag where that much flare would "bite" you. The wavering thrust may have made it less desireable, but that was unexpected for Steve and difficult to anticipate. Once lifted off there was nothing he could have done anyway.

This was primarily a real bad case of a prop stall messing up a PPC takeoff.

I hate to keep harping on this, but I know about this incident in detail having disucussed it thoroughly with Steve who happens to be a good friend. Not that I'm defending him because of that. There was simply nothing he could have done short of deciding not to launch at all.

The whole thing was related to that prop. Remove it and it goes away. Steve removed it and it went away never to plague him again even with the same exact takeoff technique.

Marty

[pararigger]

[QUOTE=mignazito]
You simply have to stop clinging to this notion of pilot error in flight in this case. Simply not so. Deciding to use this prop against my advise might be construed as poor judgement, but only if you trust me. Steve now implicitely does trust me BTW.

Mignazito.
I have read many of your post and we disagreed over in the chutes section as well and as I read here I see that you are giving out Rigging advice, prop advice and how the industry has everything wrong. you seem to be a self proclaimed expert in all aspects of PPC flight, from front forks, bearings, parachute rigging and prop power input/output.. all of that based on hvac information and some metal shop work.
I don't know you, I don't know any of your background what you have done or anything and I hate to make assumptions of any kind, but I am seeing a trend that you are always correct and eagar to tell us all that you are correct and that you have all the solutions and that no one in teh industry seems to have it right. and yet you don't produce a PPC (that i know of) parachute or prop and powerplant.
Sir you dole out information freely and when people disagree you say things like the quote above.. if we only heed your advice then life will be fine? if we don't then we are doomed?
Your advice may be correct but if it's not then you could be handing out a death sentence to those that take it.
i would invite PPC pilots to use caution when taking advice from anyone, (myself included) and do research for yourself to further understand all the risk and or benifits of the advice.
I would also invite the moderator of this board to carefully consider the content of some of these post and use wise moderation to insure safety for the masses.
Fire away Mignazito because I have to agree with Mr Yonkin on this issue, yes there may have been some prop problems, but there was a PIC and he comanded his craft skyward instead of aborting the flight and he crashed his aircraft as a result. Pilot Error!
Joe

[Bruce Brown]

As moderator of this board, I can tell you that I have known Marty for several years and he has spent valuable time with me and my personal machine correcting wing related rigging issues. I also personally know many on this board who he has done the same for.

This forum is here for open discussion and while I understand your concerns, I will not censor his posts.

I think that you really said all that needed to be said with, "i would invite PPC pilots to use caution when taking advice from anyone, (myself included) and do research for yourself to further understand all the risk and or benifits of the advice."

Just because Marty or anyone writes something here doesn't mean that the information is accurate or inaccurate. This is a discussion forum and we must decide these things for ourselves.

The debate is what makes this forum the place to come for information like this. We can all learn from it and make our own judgments.

[Snoopy_One]

I think Mig was passing information on, and was a gentleman about it. Even if I disagreed with him ,(on this issue I am ignorant so I don't have an opinion) I would still believe that he was trying to be helpful, not a know it all.

[pararigger]

I think Mig was passing information on, and was a gentleman about it. Even if I disagreed with him ,(on this issue I am ignorant so I don't have an opinion) I would still believe that he was trying to be helpful, not a know it all.

i will just quote a few of his many rants.

"Prop mechanics is not well understood by many. In fact my delving into this realm was prompted by my frustration with trying to get information from the industry about props including the prop mfgs themselves. Funny how some folks can make something they really know little about. Getting to the right "geek" in the back room is the main problem."

here is one aspect of where seems to know more then the manufacture and how they know little about a product they produce as well as calling them Geeks.

And another quote that i simply enjoyed.

"Deciding to use this prop against my advise might be construed as poor judgement, but only if you trust me."

If you don't do what he says then you are in use of poor judgement! Now i will agree that typed verbage can be construded in many ways and taken out of intended content, but there is an on going them to Mig's post and that is he is right, the industry has it wrong and he is the keeper of all ppc knowledge

[R.Bickham]

I believe Marty knows more about PPC`S than anyone on this forum. If you read any of his articles in Aerosportsconnection Magazine you will see he is very smart. I don`t know why anyone want`s to start a bunch of crap with other people on this forum. We are all here to help each other. I think this thread should be locked!

[woodyking]

Have to give credit where it's due, Marty has done great improvements on many PPC things, showing clearly that the manufacturers aren't always on top of what they are doing. I've got eight years playing with them now, and Martys' advice has been very helpful. It's easy to see where makers cut corners or compromise for many reasons, and Marty has spent lots of time working on PPCs. I'd put way more faith in what he says than anyone else I know as far as PPCs go. I've had maybe 30 of these machines, and there was always improvements that I made to each and every one of them. Every single one. Plenty of room for improvement on what you buy, and Marty has given much of his efforts to making this a better sport or hobby. Woody

[woodyking]

PS, Geek was a compliment to the one in the back who really knows what it's all about. All companies have them, and then plenty of other people to sell and take credit, but the Geek in the back is the one who makes it work.