VNE of a Dragonfly discussion on Yahoo Dragonflylist

Transcription

1 VNE of a Dragonfly discussion on Yahoo Dragonflylist I vaguely remember Bob Walters saying at an informal gathering of Df builders at Oshkosh one year (after he'd sold out to Rex) that he had tested to slightly over 200 mph without flutter, then backed off about 10% for Vne. He would not give a definite number over 200, because he said if he did, some yahoo would automatically use that as a Vne. Walters was a very conservative guy when it came to Dragonfly (unusual for a navy fighter pilot, most that I've known are the exact opposite). Richard in Chino Re: [Dragonflylist] Re: Vne And that was with unbalanced control surfaces, right? IIRC, other than the rudder, there are no instructions in the plans for mass balancing. Dave Morris That is correct. No mass balance on the prototype. One reason for the ailerons being inboard. Less efficient, but less likely to flutter. Richard in Chino... On this subject has anyone attended the flutter analysis class or used the software from: or any experience with his other classes or software. I was wondering if his classes/ software would be worthwhile. Deems Herring Might be if you're planning to design your own airplane. But if you're building according to plans, there's probably no need to, unless you just like learning stuff. If you're not building to plans, you're in for a very long haul. Ask any of us who tried. Dave Morris I do like learning stuff but I was thinking more along the lines of what has been discussed here. It seems that any non STOL design ends up with people pushing the Vne envelope. The software appears to have been used for flutter analysis on completed designs. Some designs appear to get no more analysis than "One flew faster than that once." - Deems

2 Here is a link to a white paper on HP vs Speed and design loads I just found through a google search when looking to see how fast a DF would cruise with a 100 HP Jabiru engine. What kind of figures have you all seen for the DF with the Jabiru HP engine in it?, I don't have a Jabaru 3300 in my DF but I do have a 3300 Continental. I have seen this type of chart and done some calculations 20 years ago. IIRC my DF is at the edge of the envelope at 140 kts at 10,000' using only 25ft/min gust. If the gusts go to 50 ft/min it gets into the structural damage area real quick. It has been a long time ago but I do remember that I couldn't believe what I was reading. It scared me! But I guess this type of chart doesn't mean anything to us Dragonfly flyer's because we have a composite plane & every one knows that they are designed and built WAY strong. Maybe the folks that are flying the turbo charged 150+hp Subaru's at 180 to 200 mph can enlighten the rest of us just exactly how strong the DF is! I have done my best to try and dissuade DF builders from installing LARGE engines. The 100 hp engines are plenty of power to get into the structural damage and the structural failure portion of this chart. This is easily done in a Dragonfly due to its very light wing loading. The plane likes to fly above 10,000 on just a little hp. Mine with the Cont will fly very well at 14,000' and the O-200 is not turbo normalized so the hp is no where close to 60 at that altitude. But then again, no one has blown apart a Dragonfly flying at 180+ mph at the higher altitudes so it must be OK right? I guess I'm just a chicken at heart. [end of rant] Justin ~^~ Justin, Tks for posting on that. I heard from someone, don't remember who now, but they said the G loading on the DF in reality is much higher than the published figures, I mean WAY higher. I wish I could find where that info came from and be able to confirm it. I suppose, it would make the airplane much heavier to have aerobatic G-loading capabilities. Doesn't matter much for me now, I bought a project and it is way beyond making those kinds of changes. Newbie here, as everyone is well aware of. I am asking typical questions showing the typical ignorance of someone new to homebuilts but I have to ask. Google searches help but sometimes I don't use the right search terms and give up on that and ask here.

3 Try this test report. Bob MO Yes! That's what I was hearing about. Thanks much, 10 G' minimum in their tests is incredible. I wonder how the wings on the DF compare to the E-Z's strength, anyone? Everyone, I have been reading these s and many talk of larger engines, faster speeds, and higher G forces. I am not an engineer, however, from experience you also, need to look at the smallest of parts. I will tell you of my experience. I built my DF in 1980 to I was plans number 005. I built it right to plan. I then had 10 wonderful years of flying my DF. I really miss those flights. I had several close calls over those years. I started off on my first flight as being the first person to break the canard. As the years went by my flying greatly improved. I few it several times to Oshkosh and twice to Sun & Fun from Michigan. My DF had the 1831 VW and was fine for 2 average people and a little baggage. Well to get to the point, my last flight was in late I was planning on selling my DF. I was out fling solo, just flying around for fun. I was in a step bank about 60 degrees pulling heavy on the stick. Then heard a very loud sharp bang and the plane fell out of the bank. Wow! was that a heart stopper. The DF was still flying. However, there was almost no aileron control. I flew it very slowly and carefully back to the airport using the control stick as little as possible. What had happened was that the control stick broke on one side of the Y split at the bottom of the stick. Only one side was holding and it would bend every time you applied pressure on the stick. Thank God the other side held or else elevator control would have been lost and I am sure I would have lost all control. The next day I decided not to sell my DF, instead I cut it up and scraped it. A very sad day, however I was fine and I did not want to push my luck. Also, I had built all the metal hardware myself and maybe one of the many metal parts throughout the DF may also be ready to crack. So if you increase the engine and fly at higher G forces, you also need to think of all the little parts, such as the control system etc. The little parts can kill you just as easy as the wing or canard. Be careful and have fun. Bob Moehlenkamp Bob, Is this an Apples and Oranges thing? The Dragonfly web site has always posted that this is a 4.4G positive airplane. It is also advertised to cruise at 165 mph and yes redline is 180 mph. Go past 180mph true you are the test pilot. Change anything from the plans and you are the designer and totally responsible, including paying the ultimate price for your mistake! Hopefully you do not take someone with you.

4 Not log ago, Dale Martin of Lewiston ID made available a DVD of Burt, With the help of Mile Melvil and others, testing three builder Long EZ canards to complete destruction. The first two failed a little above 12G's! The third was mikes personal (first plans built) GU canard. With a device simular to what many have seen punch test the skin of a fabric wing, The surface of the canard "skin" (not in the area of the spar cap) was intentionally damaged with a point delamination (an occipital, meaning circular,) kind of impact close to the root out to appx 8"s. This canard failed at a little over 9 G's. Gene 9:58AM CDT Sounds like we can fly these aircraft at Vne without too much worry of structural damage or failure if we hit a fps gust. Incredible. Hi, "far more g-loading than the published limitations". You don't really know that, because you don't know under what conditions YOUR canard was built. Did you do it yourself? Did someone else do it under poor conditions? In the experimental world, there can be HUGE variations between one guy's canard and another guy's. One year we measured the angles of incidence of the wings and canards of all the Dragonfly airplanes at one of the fly-ins. You would think they would have been pretty close, since the plans lay out great detailed instructions on doing so. And you would think this would be a critical parameter. But what we found was several degrees of variation between builders! A long time ago, there was a DBFN article that tested the strength of a fiberglass coupon laid up correctly, laid up too dry, and too wet (IIRC). I also recall thinking at the time that these were built to simulate the attachment points on the wing bulkhead. And I remember thinking, gee, those attachment points are pretty critical, and I wonder how many builders were able to get the optimum strength out of the layups they did. The other things you would have to worry about if you increased the horsepower would be: 1. rudder flutter and hinge strength 2. engine mount strength, bolt sizes, attachment points to stringers, etc. 3. fuel consumption I was one of those people who tried to make a few fairly insignificant changes to the design, and ended up spending 13 years and still not having my plane done. I don't recommend my path for anybody who is not independently wealthy, retired with no family ties, and with lots of mechanical design experience. There are a thousand little tiny details that will jump up and bite you in the butt for every little deviation.

5 Dave Morris Good points Dave, I knew that was also one of the variables but didn't mention it. From these unknowns if I were to purposefully break the published figures I'd be taking chances. Scary to think of an in flight structure failure. I might just end up buying someone else flying machine and work on the ebay DF project over a long period of time. Someone else has a "75%" complete DF up on ebay again using the same photograph of a flying Dragonfly you have on your page, but not the same aircraft, right? I mean, yours isn't up on ebay is it? No, mine is being shipped to its new owner on Tuesday. Dave, Because the canard was designed to also be the main landing gear it's strength is over designed when used as a wing. However the rear main wing is not. Ryan Hi Dave, Sam Hoskins did his thesis on composites here: I don't think we have much to worry about with the composite part of our structures. Both of the test were done on poor layups and passed. But, the attach points are suspect. Since it only takes one week spot, I think a parachute might be recommended for our test pilot. I think you need to keep your DF and buy a Yugo that will park in the space left in your garage. Then you will find how easy it is to make a DF work without failure. Have fun in your Mooney, but keep building. Bob MO Still, the attachment points, the engine mount and all of that is enough to keep me somewhat conservative in how far I would press one of these airplanes. I want to fly, been away from it too many years so I might just buy an airworthy DF being offered to me at a very good price... assuming the deal he just jumped on goes through. I just have to convince the boss to let me do it and sell a bunch of my other goodies and pull some cash from the house refinance that we were planning to do anyway. Price is very right but I'd have to leave the airplane where it is until I was able to come back up to speed, get re-cert in a performance aircraft and get some time with a pilot in the machine itself before trying to fly it home to Alaska, some 3000 miles. Buying this machine is up in the air right now on both ends from what I can tell, depending on some things so it might not happen but sure is an attractive idea.

6 , All DF's are a steal! Where can you buy a finished plane for half of what it takes to build. Lands like a Cessna (sort of 48mph???), faster, and great MPG. Cessna's are rated for 2.7g's!!?? Fuse is 43", 6' pilot. You build for personal gratification (and your friends think you have lost your mind). Building is not cheaper!! But, the satisfaction you gain "is priceless". The only difference between buying an experimental and being the original builder is the Repairman's Certificate. You have to pay for an Annual. Probably should have a second set of eyes anyway. Want to fly NOW! Steal a DF. Build your project and you have the only DF's north of Canada. What was your VW motor like? Did Charlie look your project over? Bob MO It sure seems that way, low prices for the money and time put into them. I have been told that the engine which came with this ebay DF originally came from a fellow in New York. Charlie AKA OneSkyDog knows some of the history on it. It's a 65 HP HAPI without ignition or carb but does have the exhaust and engine mounting (which I haven't confirmed fits the engine yet). I don't intend on using the engine and have an unspecified ($$$) offer for it by someone who is building a single place homebuilt so he can have some spare parts for his other 65 HP VW engine but at this point in time I haven't priced for sale because I am thinking I ought to keep it for awhile before doing that because if I chicken out on finishing the ebay DF it would help it sell, even if underpowered. I hear that these 65 HP HAPI engines are plentiful and don't bring much money these days, probably for the same reason I don't want to use it, need at least 85 HP for the DF. Dave, I am sorry to hear you are out of the build. Best of luck on whatever you do. Come for that visit and we will do a fly over of the Cape. Andrew in sunny FLA The good news is that the Dragonfly and Corvair engine are going to good new owners, and that I've located a Mooney that I'm in the process of acquiring. So I should be able to make it to the next Field of Dreams the way I've wanted to for the last 13 years: by air. :) Dave