wingsman

After I was only able to reach speeds of 115mph to 120mph on my DD with a GRRT, I decided that there was a need for a change. I basically reduced the drag by making the wing thinner from the middle rib to the center. This reduced the drag and performed MUCH better. I used my Eagle Tree FDR (flight data recorder) to compare the differences. Here are the results...

7.2 X 8.3 APC 137 MPH
7.2 X 8.6 APC 147 MPH
7.4 X 8.0 CF APC 144 MPH
8 X 7 APC 154 MPH

Using 10% Omega pink.
I am working on a prop that will be a 7.0 X 9 that will hopefully get 150+. I also have some pics while it was under contruction. These are before and after shots. Notice how the wing is much thinner. This also greatly increased the response of the elevons that I had to back the throws down to factory settings!
The modifed prop....
7.0 X 9W APC 137 MPH
6.8 X 9W APC 147 MPH
6.75 X 9 W APC 143 MPH

wingsman

These are some construction pics. I permantly installed a pitot tube in the right wing for airspeed. The servos are Hitec 5475's that help resolution for trimming at hi speed.

Mike Connor

My Feedback: (5)

This should be interesting. I predict the speed will stay the same or be slower with the 7" prop. I think the Dust with everything hanging out needs a larger diameter prop.

bob27s

My Feedback: (19)

Try the carbon QM40 prop, APC 7.4x8

soarrich

My Feedback: (98)

It's good to see someone getting real data on speed rather that, Look's about 200mph!

I don't think the DD airfoil helps any in the quest for speed, so I picked up a delta off ebay that has a smooth airfoil I'm going to try an OPS .60 with a 9x12 on it.

I think someone is going to realize the way to go is electric, my little delta turns 59,000 rpm, giving it a top speed of 167mph in theory,222mph with 4 cells. It's too draggy for that, but I drag raced a Hobby Lobby Mig 15, we came over the end of the field slow, both went full power and by time the Mig 15 got to mid field I was starting my vertical out of sight victory climb at the other end of the field. The field is about 400 feet long, and the Mig has been radar gunned at 65mph.

Troy-RCU

My Feedback: (1)

Putting a fairing around the motor would do more than anything you could do to the airframe. Your airframe cross section looks good, the motor looks like a speed brake.

wingsman

Hopefully, I will be able to find out this weekend. In theory, with less drag than the "fat factory thick" wing, I should be able to get away with less diameter. My last test with the "modifed" 7.2 X 9 prop, the GRRT would not stay on the pipe for more than 7 or 8 seconds. I will try shaving it down to a 7" and see if stays on the pipe.

combatpigg

My Feedback: (3)

You're on the right track as far as props go, you gotta play the hand you're dealt as far as the engine is concerned. A fairing will allow even more unloading, with aerodynamic improvements you can get away with more prop load. I tried to cut down and recontour the 7.2x8.6 and the plane [90% DD] got slower. With a KB 6.5 launched at 24,000, its' best clockings were with the standard 7.2x8.6 APC.

MyWay

You might try a APC 8.5x7.25 on that GRRT. Good combination of rpm and thrust.

combatpigg

My Feedback: (3)

If you do that, you will gain all around flyability, but not gain any speed. My favorite prop for carefree launches, easy needling and all around sport flying is the 8x8, this is with the power that I have available. A 7 inch prop with a lot of pitch won't carry this much plane much further than a 315 foot timing zone [after a dive], but that's enough distance to get relevant speed figures with walkie talkies and a stop watch.

wingsman

I did some more carving and testing this weekend and posted the results above in the 1st post. The best that I have found so far is the 8x7 logging at 154 MPH. I may try an 8x8 for grins. I have a high speed trimming problem as the dd tends to start a right roll when the speed peaks. After fixing this problem, I plan on mounting a Formula 1 Nelson that runs 50% nitro. It drove a Kazi Killer pylon racer around the track at 157 and the right wing snapped and broke loose in level flight! It should be awesome.

My overall goal was to modify the Diamond Dust which was peaking at 120 MPH, to achive 150 MPH without increasing horsepower. The only option I saw was to decrease the drag. After I make some test with the Nelson, I will post the results. Probably around the holidays.


Thanks for the comments and feed back. I'm not sure how I can cover that "Speed Brake" to reduce the drag even more.

Does anyone have any accurate speed results on Diamond Dust?

HighPlains

My Feedback: (1)

That would be about 15 mph slower than what top F1 airplanes did in full race trim.

Mike Connor

My Feedback: (5)

My first Dust started doing that after about 80+ flights. I stripped the covering off twice looking for the problem and reinforced many areas and never did fix it. After the last flight I didn't have to worry about the trim problem (see photo). I finally built a new one and things were fine. I would be very interested if you do find the problem.

MMallory

My Feedback: (1)

Everything bends at those speeds. I reinforced the verticals to get mine to stop rolling as much. The soft balsa elevons were also flexing. It could be one is harder than the other causing your problem.

Mark

combatpigg

My Feedback: (3)

I predict about 180 mph for the Nelson powered DD, which in a drag race puts it right there with a F-1 and the same engine. I just got 177 mph out of a K&B 6.5 on basically the same plane as Wingsmans' [I used 50% nitro, too].

wingsman

Sadly, we did not get to tweak the Kazi out before the wing came apart. We were testing a prop when it crashed. Most reports of the Formula 1 machines were making speeds in the 180's.

Sorry to see your loss. I had this problem before I recovered the dd, and was able to correct it. The right wing had some positive incidence (I belive) where the front was slightly lower than the rear, and would start to roll right at high speed. I was able to twist the wing up, and shrink the wrinkles to hold it straight. I will need to check it again as I suspect something is warped.

I actually had one fin break off in flight (in its first life) and I reinforced the fins with carbon fiber. I landed with no incident. I used oversized elevons (not the stock ones) that was cut from one piece, but I will check to see if one flexes more.

That same engine (Nelson) boosted a Q500 from 140's to 170's. I hope that what it will do 180 mph and stay glued together!