Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

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Old 02-13-2008, 09:56 PM
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haikt
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Default speedy

Hello all,
I have posted some SW pictures here some time back.
I have made some progress on the speed plane I was working on, It has a MVVS .15.
I am wondering what you all think, amy coments are welcome.
I have ordered some 6X5 6X6 and 6X6.5 APC props, which one will you recomend using for speed or any other prop.
Let me know what you all think, about what speed will I get out of it and what RPM's can I get form MVVS
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Old 02-13-2008, 10:15 PM
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Default RE: speedy

Nice looking design. What are the specifications in wing area, span, weight.
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Old 02-13-2008, 11:05 PM
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haikt
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Default RE: speedy

wing is about 230sqinch I am little high on the weight its at 1.5 pounds now should be around 1.75 when done.
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Old 02-13-2008, 11:42 PM
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Default RE: speedy

That's light and small. Speed estimate? I don't know very much about that engine, but the old QM15's (much heavier, bigger (300 squares)), with Nelson 15's did about 130 mph. We ran something around 25 K on the ground with about a 6 1/4 to 6 1/2 diameter prop at about 5 1/2 pitch. You may be able to push past that by a significate amount.

One point about many of these speed designs, both conventional and delta. There seems to be quite a few with the pipes enclosed with vents or whatever to exhaust the heat of engine and pipe. I'm not too sure that that is going to be the lowest drag configuration.

The reason is due to surface area. With the pipe running down the fuselage, you have to consider the surface drag, both on the outside of the pipe cover as well as the inside of the pipe cover and the pipe as well. It may be that an exposed tuned pipe with a small pressure cowl around the cylinder may offer lower overall drag.

On the other hand, heating the exhausted air from the pipe cover might produce a mild amount of thrust. And perhaps some engine/pipe combinations may need to hold some of the heat in the pipe to operate properly.

One of the interesting things is the fact that adding heat to a constant diameter tube helps keep the air passing on the outside laminar.
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Old 02-14-2008, 12:05 AM
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Default RE: speedy

I think the real answer on the props is which one will work best with the pipe setup. I'd lean to the 6-5 for first runs then see if the engine pulls the higher pitch without the pipe being too long. The engine will handle the rpm of any of those so my tendency is to start with the lighter loads and work from there to avoid overheating the engine, esp. as I assume it is new.

Some of the Euro RC speed guys running 2.5cc get the speeds way up there, as in well over 150 mph IIRC. Other than visibility, I don't see why not, after all, FAI control-liners crack 200mph and that is no mean feat dragging the line around. Those same engines should be able to motivate a well designed RC model at firghtening speeds. You gonna put a remote fuel cutoff on that thing in case it starts to get away from you? It's a small airplane! Or is this every day fare for your thumbs?

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Old 02-14-2008, 10:39 AM
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Default RE: speedy

beautiful project
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Old 02-14-2008, 11:21 AM
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haikt
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Default RE: speedy

The fastest I have gone before is aroun 120 with an eliner. I used to fly combat open B for a while and they get up to 100+ .
As far as cut-off, first I am going to fly with the rc carb on to make sure the plane is set up and build ok, once and if I get used to the plane I will put the ventury on to get some more from the engine and have to set up some type of cut -off.
Way back when I got into model airplanes I started with F1C free flight models, for cut-off we used to have a pinched fule line going to the carb and when ready to kill engine it injected fule into the carb to kill it. otherwise the glow head would burn up every time. those were hot Rossi 15s with 1 blade props running around 40000 rpm, 5 sec. and the 2 pound airplane was out of sight on vertical
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Old 02-14-2008, 03:03 PM
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Default RE: speedy

Haikt:

Real sweet? I want one, but in 90 size so I can see it, Ahhhhh, well, maby 120 to 180 these days. ENJOY
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Old 02-15-2008, 12:09 AM
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Default RE: speedy

for some reson I like small planes, I have big planes but seem to have less fun with them for some reason,
Small ones are hard to see, I need to make this plane bright, like red and green, I dont know yet, first I think I am going to fly it without top cover and paint might paint some stripes on it, I hate to spend all that time and effort to find out it does not work.
One thing that concerns me is the initial hand lunch, I dont know how it will do, I was thinking about making a little cart like CL people do to take off from ground. The wing is small for the wight so it might stall WHat you all think.

I have glassed the fuse and primed the cover all the servos are in, I had to machine a backplate and a ventury for the engine, I dont like the plastic backplate that came with it.
Looks like I will need some weight at the back, Servos and battery are as far back as possible.
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Old 02-15-2008, 05:55 AM
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Default RE: speedy

what device would you use to record realtime speed remotely ?
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Old 02-15-2008, 10:37 AM
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ORIGINAL: haikt

The wing is small for the wight so it might stall WHat you all think.
As HighPlains pointed out, I would not consider 17.5 oz wing loading high on this type of plane.
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Old 02-16-2008, 11:50 PM
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I had a good day of building today, got over my cold somewhat and spent the day in the workshop.
I have it to the point that I can test fly it, Its all in primer and set up. took me some time to get the CG right had to put some lead in the tail.
Got the pipe hooked up, it was to close to the ail. servo and the tank so I had to get some heatsheild, will see if this stuff works.
I ran the engine today, not very happy with how it runs may need brake-in. It is getting around 18K with 6.5X5 I have to put lighter prop on it to brake in.
I had to get 5% nitro because I read somewhere that MVVS likes this stuff, anyone know it its good or do I have to go to 10%.
I had to make a special battery to fit all the way in the back to get CG close.
Also the RC carb looks to small, I mean the hole is small, I have to try the Venturi I made to see how it dose. I might have gone little over with the diameter of the hole in the Venturi, I have it at 9mm to the 4mm used on the stock one. May have some fuel issues, but I have stock one form other engine and can use that.
Now I have to get my nerve up to go and try this thing.[&:] I usually know what to expect from a plane and get ready but this is all new and experimental so I am little .........
If we get some brake form all the snow and rain tomorrow I am going to fly this thing, this way no one will be at the club and I can at least be safe.
I will take some pics of the test flight if I get there..[:'(]
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Old 02-17-2008, 12:50 AM
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Default RE: speedy

Great looking project! I'm partial to small planes too. About the launch, feel out the thrust that you are getting VS the planes' weight as it runs in your hands. Some plane / prop combos need a pretty hard, level throw.
To get started, I think you want to pick a prop that gives good thrust, like maybe a 7x3? Problem is we don't know if that engine will exceed the rpm limit of 190,000/diameter for APC sport props, it will probably come close? Once you get the plane dialed in with a thrusty prop, then start testing smaller props with more pitch. That plane isn't much larger than a AMA rulebook 1/2A pylon racer, but it weighs about 3 or 4 ozs more. Those planes flew well with 4.75-5 inch diameter props, but the launches were "rubbery". I think your design is stretching the limits a little, which is good work on your part.
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Old 02-25-2008, 07:39 PM
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Default RE: speedy

Well I got the plane in the air this weekend, was interesting....................................... .
First day I went out to try it and it was cold, no people so I thought good day to do it. Engine ran great, was getting RPM's around 25K with 6X4 good pull. lunched it by hand and very good. was nose heavy but ok. on a turn back to the runway engine cut off and the thing just kept going straight, could not turn it at all hit a tree......[:@]
not to bad got home glued back togethjer and put in more ail. but while in the air it was FAST very fast.
Got back next day and started the engine ran good took off engine quit and I crashed,
[:@]
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Old 02-25-2008, 08:44 PM
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ORIGINAL: haikt

Well I got the plane in the air this weekend, was interesting....................................... .
First day I went out to try it and it was cold, no people so I thought good day to do it. Engine ran great, was getting RPM's around 25K with 6X4 good pull. lunched it by hand and very good. was nose heavy but ok. on a turn back to the runway engine cut off and the thing just kept going straight, could not turn it at all hit a tree......[:@]
not to bad got home glued back togethjer and put in more ail. but while in the air it was FAST very fast.
Got back next day and started the engine ran good took off engine quit and I crashed,
[:@]
More bench running time for that engine/tank setup maybe?

Cool that you've had it in the air. What state is it in now after the second crash? Will it fly again? You've certainly earned your merit badge from this forum with that little speedster.
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Old 02-25-2008, 10:36 PM
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Default RE: speedy

My first guess is that it is too nose heavy to glide.
Low speed control response might need to be bumped up with high rates?
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Old 02-26-2008, 12:30 AM
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Oh I took the engine apart and piston and sleve are dead, looks like ball bearing came apart or something, cant find the reason yet. Its all scored, ordered a new piston/liner combo. looking to build something little bigger to get the engine/pipe/fuel figured out first.
As far as the plane its ok, needs little work but can be used again, the wing is ok.
I will build another one soon maybe mold the fuse, I work long hours so dont get much building time.
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Old 02-26-2008, 08:25 AM
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ORIGINAL: haikt

Oh I took the engine apart and piston and sleve are dead, looks like ball bearing came apart or something, cant find the reason yet. Its all scored, ordered a new piston/liner combo. looking to build something little bigger to get the engine/pipe/fuel figured out first.
As far as the plane its ok, needs little work but can be used again, the wing is ok.
I will build another one soon maybe mold the fuse, I work long hours so dont get much building time.
Ouch, the engine fragged already? 25k shouldn't kill it. But I'd get a little bit of test stand time on the repaired engine and pipe combo to make sure everything is chickitty-boo. You got enough to handle test flying that little speedster without worrying about new tight engine issues at the same time. Like CP suggested, take a good hard look at the CG - while a fast airplane will groove around all day just fine on a forward CG with just a touch of trim due to high airspeed, you gotta retain handling and flare capability for landing, not to mention hand launching. If the CG is way forward even launching can be a skitterish affair until you reach a flight speed where the nose will stay up.

Nice work on this thing, I bet a bunch of folks here are waiting for the followup flight reports. Now, can you fit a .21 in there?

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