Richardfast

My Feedback: (15)

I just broke in my TT .40 pro amd I am flying it on a 48" wingspan World models plane (Spitfire Kombat series). My TT .40 turns an APC 9x6 at 16,300 RPM on 15% nitro synthetic fuel (man am I happy with my $75 investment!). My friends and I estimate the speed of my plane at about 75 to 80 mph. This corresponds pretty well with a 6" pitch prop turning about 16,000 RPM (90 mph pitch speed with 80% efficiency). Where in the world are people getting 110 + mph in AMA 424. There is no way a 16,500 rpm limit on a 9x6 prop can go that fast! Am I correct here?

HighPlains

My Feedback: (1)

Richard,

In general terms, the 16,500 rpm limit is while on the ground. In this condition, much of the propeller is stalled which is a greater drag on the engine than when it is in flight. Depending on how clean an airplane is, and the timing of the engine, it can unload in flight 2-3,000 rpm or more. Most propeller pitch is referenced to a flat blade, while the airfoil pitch may be higher. Also, 80% efficiency does not mean that a pitch of 5� would only go forward 4�. Rather it is a measurement of the conversion of engine power to thrust. Most props are in the 65-85% range.

For a given airframe drag and propeller efficiency, engine power determines the top speed. Increasing the power by 50% only increases the speed by 14.5% since it is a cubic function. For an airplane to go from 80 mph to 110, part would be due to the engine being able to unload more due to lower airframe drag (thus making more power). The rest would be due to the lower airframe drag giving less propeller slippage.

Just because your fuel claims to be 15%, it may not really be 15%. Some fuel manufacturers measure by weight, whereas others by volume. Since Nitro and oil weigh more per unit volume than methanol, you end up with “15%� fuel that is really only about 12%. Volume measurement is the only honest way to measure, but cheaper fuels often use the other method. Most pylon flyers prefer to use just one brand of fuel, because they trust their expensive engines to a brand that has enough oil and a true 15% nitro

Richardfast

My Feedback: (15)

Highplains,
Thank you very much for your very informative answer to my question. I will soon be purchasing a Viper 500 for my TT .40. I am sure there will be less drag than with the Spitfire. This is the fun of the RC sport, isn't it?

DHG

My Feedback: (7)

Richard,

Welcome to the silly & fascinating world of racing! I see you're from Grass Lake, Michigan. I spent 20 years in Ann Arbor, and the guy who taught me to fly R/C moved to Grass Lake. I doubt if he still flies, but if you get a chance, say hi from Duane to "long walkin', slow talkin'" Don Wilke, ham license WB8BKC. That's what we do in this business, corrupt the nation's youth. [8D]

Richardfast

My Feedback: (15)

DHG,
I don't know the person who you are asking about. I do know some older gentleman from Grass Lake (I am also an "older" gentleman, but I have only lived here for two years) so I will ask them. I was flying IMAC for awhile but I have become discouraged with my lack of ability and the high cost of a crash. I guess I just can't enjoy buzzing around the sky, I have to have some kind of target to shoot at. That's the way I have always been. RC is a great place to be that way.
Richard

diggs_74

The problem with the target is that it's usually on/is the ground..... The good thing about the target is that it's usually pretty easy to hit....

Bozarth

My Feedback: (15)

I saw 105 mph this weekend in Medford, OR via a radar gun. TT40 on a Viper or Predator (not sure). This speed was obtained just prior to the plane turning at #2.

Bill Vargas

My Feedback: (5)

I heard it was a Racer II that won the 424 event there in Oregon


BV

HighPlains

My Feedback: (1)

Wow, 105 mph? Is the TT40 THAT gutless? The Viper/Preditor THAT draggy? Or does the 9-6 prop hold down the speed THAT much? I mean, that that speed would only require about 3/4 hp (compared to 2.8 hp in a Nelson).

It must be the prop size. I've seen 25 powered quickies do 100 with open selection of props.

luv to race

My Feedback: (1)

I could swear that about 4 or 5 years ago, that guys where saying that Tim Lawlor's V-Max went 120-125 with the TT40...? maybe that was a spoof?

daven

My Feedback: (1)

I believe 120-125 is possible with the TT on the long course.

Were using the O.S. .46 and get 120-130 pretty routinely on the short course (475 feet).

PylonWorld

Bob,

Yes, the APC 9x6 Sport prop is not the ideal prop for the sport .40 engines. Speed picks up significantly if you use an APC 8.5x7.0 Pylon prop. And if you use a non baffled muffler, you get even more. Using a tuned muffler and an APC 8.5x7.5 Pylon prop gets things going, but only to about the speed of a sport .46 (1.7hp versus 1.2hp).

I have never accepted the 120+ mph figure that some people have used. Maybe on a long course, or out of a dive.

HighPlains

My Feedback: (1)

Well 105 would mean that the TT40 is unloading about 2000 in the air to around 18.5K. This seems reasonable.

To achieve 120, you would need to unload about 4500 rpm. This also seems reasonable if the airframe drag is low enough.

A slight wind or slight dive would change things alot You would also need to launch pretty rich so you have enough fuel at the higher RPM. One problem with that much unload, the engine might be past it's peak hp.

So it is most likely the Preditor/Viper are not the equal to a better airframe. I guess one method of telling is to compare the glide of each. Who wants to put them up with a High-start? Shoot them up and the last one down wins the low drag contest.

PylonWorld

Bob,

The Viper is definitely faster than the Predator in my experience. The airfoil on the Viper is a new design by Michael Selig especially for Q-500. It is very easy to tell in the glide to landing that the Viper has a much better airfoil. It is harder to get slowed down, and it glides forever.

I'm so impressed by the Viper airfoil that I'm going to get another Viper and make molds off of a stripped, prepped, and glassed wing.

The Viper wing is heavy though. Unlike the Predator wing which has no spar of any kind, the Viper has basswood and carbon fiber. But it is about 4-5 ounces overweight. Therefore it is hard to get a decent weight on a Viper even with high torque micro servos, a light receiver, and a light battery pack.

I should be able to make a composite wing that will bring the weight down. And if I sell any of the wings, they will be very nicely priced.

If you have an "ultimate" Q-500 airfoil and wing planform, I would be interested in doing a mold and wings if you are willing to let it "go public".

Richardfast

My Feedback: (15)

As the "newbie" that started all of this, I thank all of you for your enlightening remarks. I just received my Lanier Dominator 500 kit today. I like to build so I thought I would give the Lanier a try, instead of the Viper ARF. When done and flown using Sport Quickie rules, I will let all of you know the results. I have a feeling that getting down to 3 1/2 lbs will be the biggest challenge. I am going to go with the "V" tail and use the Hitec Micro flight pack (HS-81's, 555 rcvr, 250 mah NiCds. Anyone having built one of these, that likes to give out some pointers, is sure invited to do so.Thanks again.
Richard

Bozarth

My Feedback: (15)

Regarding building the Dominator, I found it easier to abandon the sheeting supplied (24" long) and replace it with 48" sheeting. I glued the foam wing cores together prior to sheeting. I then sheeted this "single core" with the 48" sheeting. I then glassed the center section in Revlution fashion with recessed wing hold down bolts. I also moved the v-tail controls inside and glassed the rear portion of the fuse before covering. Seems to fly fine. JR 341s for the tail, Hitec 225 on the ailerons. Good luck.

Kurt

JohnBuckner

My Feedback: (1)

Richard may I suggest that the HS-81 is of sufficient torque for flight but the gears are not up to the task with any kind of hard landings or whoops. I beleive you will find yourself stripping gears all to frequently. The HS 225 is far more preferable and is the most popular servo for Quickees. I tried them at one time and soon discarded the idea. The 555 is a great Rx and I have around 15 of them mostly for the
racers. Probably the most common set up is a 555 (which will work well with the antenna wrapped on a straw or doubled forward and then back to keep it internal) three HS 225's, a HS 85 for throttle and a 270 pack which will get you through six rounds.

John

daven

My Feedback: (1)

John gives great advice. The 81 gears just don't seem to hold up, if you are determined to use the smaller servo, at least go with the Hitec 85's with Ball Bearings. They seem to last longer, and most likely would be ok for sport pylon.

The 225s are slightly heavier, but basically bullet proof in this application.

The Dominator is a good flying Quickee. I actually prefer the standard tail version to the V-tail for anyone new to pylon racing. Much easier to build and to get the tail incedence perfect. I would suggest glassing the nose, with the thin firewall it is susceptable to coming loose.

Good Luck.

HighPlains

My Feedback: (1)

Richard,

I guess that I will admit that I have used HS-81 servos in 428 quickie, and the HS-80 servos in another one as well. They have plenty of torque (you must use two on ailerons) and for the V-tail. But I don’t recommend using them, even though I have had no problems with them. For one thing, the output shaft is not supported by a ball bearing, and after a fairly short time, you will see the output shaft develop slop. I flew the HS-80’s for about 50 heats before a mid-air took out that plane. The wing survived, so I build another fuselage and flew it with a ST 40 and an ultrathrust muffler for another 10 hours. The servos worked through all of this just fine, with just the output shaft wear.

I agree with Dave that the HS-85 servos would be much better due to the ball bearing output. When I use the small servos, I drill a new output hole as close to the center as possible (inside the factory holes). This gives the servos a better mechanical advantage. To go around the output mounting post, I place a slight bend (about 15 degrees) in the pushrod about ½ inch from the z-bend so that the pushrod doesn’t bind.

The HS-225’s are also good. I have used them a lot in 428 Quickie, and Q40. In sport flying, I have used them for over 150 hours of flight before failure. Then two quit within about 10 hours of each other. They also have a ball bearing output like the HS-85.

Bob Dible

garys

Bob,
How do you get 10 hours out of a pylon racer? I doubt that I have 10 hours of pylon racer time over the last several years combined! My last four racers (two Q500's and two Q40's) probably didn't have a total of an hour between all of them!
GS

HighPlains

My Feedback: (1)

Gary,

It would be at a minute at a time.

After the mid-air, I didn't trust the wing. So I built another fuselage for it and sport flew it with the ST40 and ultrathrust just to test the servos. That's about the only way to get 10 hours. I stopped at 10 hours because of a cartwheel landing. Then last year in a moment of weakness, I put it back together to race in Denver. Figured that up there I just wouldn't be going as fast so the wing should be ok. It was, right up to the mid-air and ground thumping.

You never know with racing, sometimes a plane lasts for a season or two. But you still average a couple, three, or four a season if you go enough years. If you are breaking more than that...have you tried video games?

garys

Ok, so you cheated to get the 10 hours! I figured with just over a minute for a heat, and close to two minutes (at most) of trimming/gliding afterwords), you'd need 200 flights. I've had some airplanes last a long time, but I seriously doubt they made 200 flights.....
GS

HighPlains

My Feedback: (1)

Not cheating, just testing.

Oh I've seen a few people with airplanes that must be able to collect social security. They fly like beginners high and wide where mid-air's never happen.

You might think that people are always bummed out when they collide, but one buddy was so proud when it happened to him. His reason? He was finally in the groove enough that he was mixing with the "fast guys". I was a little less happy, it was my engine!

Richardfast

My Feedback: (15)

Gentleman,
Thank you again. I am glad I waited on which servos to use. I was a little worried about the 81's, so that is why I asked the question. Also, I am thinking about the comment on going with the straight tail until I get more experience. I am starting on the wing tonite.

HighPlains

My Feedback: (1)

Rich,
If you go with the straight tail, you should use a HS-225 servo on the elevator. If you use one servo for ailerons, then the -225 again. Rudder and Throttle would be fine with the -81's. On the V-tail, then the -81's will work, and use two -81's on the ailerons.

Bob