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  1. #1
    Mike Switzer's Avatar
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    Flight Testing - Airframe vs Personal Parachute

    I figured i should start a new thread for this subject, didn't want to confuse the other one.

    I was doing more research last night, BRS says on their web site that airframe parachute systems for experimental aircraft range from $3000 to $12,500

    I decided to look & see what Spruce was selling personal parachutes for, they run from approx $1900 - $2600

    I am looking at this a couple ways, 1) after spending a lot of $$$ on the project it would be real nice to be able to save it if there is a problem in testing, but 2) if it has a serious flaw is it worth saving, and the airframe chute adds weight & forces design compromises.

    I figure if I need a chute it will probably be in the flight testing phase (unless there is an engine failure at some time later)

    Another point to consider is the testing will be done in Central Illinois, there are lots of big flat fields around here.

    Anyone have any thoughts? Should I continue trying to fit an airframe parachute or should I just wear one for testing? (I may decide to wear one anyway just in case, even if it has an airframe chute)

  2. #2
    rosiejerryrosie's Avatar
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    My thoughts, and only mine, regarding parachutes. The only time I would deploy an airframe parachute is when I have experienced a catostrophic airframe failure. If the airplane is even glidable, glide it to the ground. Remember, once that chute is deployed, you cease to be a pilot and become a passenger, with no means whatever to influence where you land. As to a personal parachute - it will also add weight to your airplane (unless you plan on leaving it on the ground), is likely to be uncomfortable and may not even fit into the cockpit of your homebuilt (usually not much room in those fellows). If you have a lot of off airfield landing possibilities and are concerned about weight, I'd opt for a really good inspection of the airframe, to ensure that the wings aren't going to come off, and do your test flying where you can land with minimal chances of running into a tree, fence or high wires. If you take my advice and it comes to disaster, I will deny ever having said anything like this. Someone else must have hacked my computer.....

    PS. Whether you deploy an airframe parachute or a personal parachute, remember, you must be high enough for the chute to fully deploy, otherwise it will do little to save you or your airplane....
    Last edited by rosiejerryrosie; 11-07-2011 at 08:42 AM. Reason: Adding a PS.
    Cheers,
    Jerry

    NC22375
    65LA out of 07N Pennsylvania

  3. #3
    Mike Switzer's Avatar
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    Jerry, my main concern is an unrecoverable stall/spin situation. As long as I make good welds airframe failure shouldn't be a problem.

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    It would help to know what you are building. The flight test program for the n-th one of a design or kit that has a lot of flying examples is organized differently than the flight test program for an original design.

    There are much more knowledgeable folks out there than me, but I will offer the advice that slow flight, stall, and spin testing is a step by step, incremental process. If you do it that way, you are much less likely to be surprised than if you load the airplane up, blast off, and see what happens.

    The FAA has an Advisory Circular titled Flight Testing Homebuilt Aircraft. You might give that a read.

    If you intend to try a spin in your new aircraft are not completely comfortable doing all of the possible types of spins, I will suggest getting some training. Aircraft spin behavior is an very interesting topic that has gotten many thousands of man hours of investigation.... and every new airplane is still handled very carefully when the flight test program gets to that topic. If you have never seen a power on flat spin from the inside, you should pay someone to show you before you try spins in your new pride and joy. Its is much better to be over-prepared than find youself going "oh wow what do I do now". I hope that you will consider such training in preparation for your first flight as part of the educational experience.

    If you are building a design that has many examples already flying, and you pay attention to rigging and CG, you make it much less likely that you will be using your parachute. A large part of spin behavior is a function of CG, power, and rigging.

    Best of luck,

    Wes
    N78PS

  5. #5
    Mike Switzer's Avatar
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    It is pretty much a new design - loosely based on a LongEZ but bigger (slightly wider & longer with a baggage compartment behind the rear seat). Greater lifting area to compensate for weight. The preliminary numbers say it will be OK, but you never know til you fly it. And I'm using tube & fabric.

    I can't go any farther with the structural design until I figure out where the chute is going (or if I have one), so this is a major factor in the design.


    Oh, and I don't PLAN on doing spins, but if it does it may not be recoverable if the aerodynamics aren't right.
    Last edited by Mike Switzer; 11-07-2011 at 12:59 PM.

  6. #6

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    I will suggest that Martin Holman's Test Flying is an excellent starter book for someone like yourself.

    I will also suggest that a typical back parachute weighs 15 lbs. You can go to the different parachute manufacturers web sites (Strong Parachutes, National Parachutes, Softie, etc.) to get exact weights if you need them. Having worn a parachute for many years for different reasons I will advise that mind set is very important. Your flight test should include an altitude floor for abandoning the aircraft if you are not in normal flight. Successful use of a parachute requires the mental commitment to use it at a predetermined time. Time won't be on your side.

    I recall Sport Aviation had an interesting article about some of the issues with, I think, Velocity aerodynamics and a test flight the got into a deep stall situation where the pilot rode it down to the Gulf of Mexico and tried the aircraft out in boat mode. My memory of the article is a little hazy but I recall that it is worth reading.

    Best of luck,

    Wes
    N78PS

  7. #7

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    I would have both personal and airframe chute for testing. Reason - while spin testing a local design here in South Africa the plane got into an un-recoverable spin. The airframe chute was deployed but failed to be come out of the aircraft. The two test pilots then had to exit the aircraft and were saved by their personal chutes. Had they relied on the airframe chute they would not have survived. Do you know your airframe chute will work properly? Theirs did not.
    Neil

  8. #8
    highflyer's Avatar
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    An airframe parachute is a design decision and typically requires airframe modification for it to work properly.

    A personal parachute for the test pilot is not a bad idea. Particularly for flutter testing, and spin testing. I do not own my own personal parachute. What I have done is contact a local skydiving group and see if they have an older chute that they will rent out. The fixed me up with a nice thin pack chute and only charged my $25 for a days rental for the relevant flight tests. I have had more than one engine failure in my career and have never needed a chute for an engine failure. If fact, I never even damaged an airplane because of an engine failure. Your mileage may vary.

    I know there is a skydiver group in Vandalia, Illinois. There may be others closer to your location.

  9. #9

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    What About a Spin Chute?

    No one has mentioned a spin chute, much smaller and goes out the rear to get the pointy end going forward again. Most designs can be later released when things are back under control. When using a whole aircraft chute or a personal chute, the last thing that should be on your mind is the airplane (save that precious cargo). One can't go through ALL the scenarios, but try. For example, will the whole airplane chute work if the airplane is spinning (and/or tumbling, inverted, etc). In addition can you personally get out of the airplane if you had to? And practice that over and over and over.

    I talked to a guy at OSH one year about getting out of his Berkuit (sp) - long EZ type airplane. He had a small hole through the panel area that his legs stuck through (no walled tunnel for his legs). If the airplane were in any other attitude than straight and level (not normally the condition that one is leaving the airplane under), his legs would have been stuck (flailing around) behind the panel.

    As mentioned earlier, a canard should be designed so the canard stalls first ... always. All single engine TCd airplanes are fully spin tested (regs ... with some exemptions like the Cirrus designs). No multi-engine TCd airplanes are spin tested (no regs). And, before I get flamed, yes military fighter jets are all spin tested ... their flight envelope is a little different.

    Great discussion.

  10. #10

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    I work with a gentleman who was the former chief designer at Piper. He tells me that spin chutes were mostly a failure in use. I understand that a number of anti-spin devices (small parachutes, rocket motors, etc) were tried and none were found to be reliable. Did not go into the specifics with him. The bottom line was that the Piper flight test staff wears parachutes and plans to exit the airplane if needed. For what it is worth, large scale RC models are used to do a lot of the pre-first flight evaluation of the potential spin characteristics of new designs. If you are really concerned about how your original design might perform, work the math to appropriately scale it down and build a flying model. I understand that Burt Rutan started that way.

    Oh, and yes light twins are in fact spin tested. I have had some interesting and educational discussions about spin testing twins with my co-worker. But I do not suggest that you explore that topic in your own airplane.

    Best of luck,

    Wes
    N78PS
    Last edited by WLIU; 11-16-2011 at 07:18 AM.

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