Daryl Lane

Yes another speed run with a whiplash-Jett combo. Plane Whiplash,engine Jett 45R,fuel 20/20,prop 9-7.5 APC, pilot Paul Lott. Wind less than 5MPH,Temp 70,To record speed Jet-traps and radar gun, Stalker pro ATS.Speed recorded with jett traps 206.6,with radar gun 216.0.If the guys don't believe these numbers, then you need to come and see this plane in action in the spring at the speed trials. thanks Daryl Lane.

ChuckAuger

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Oh I totally believe your numbers..No doubt!!

It's just my numbers that I don't get.

Maybe if you would post you static RPM's I could start to grasp what is needed to obtain such impressive numbers...I can't get within 50 mph of yours.

Daryl Lane

Yes in a dive 206.6,Flat and level 195.3,needs more prop but hard to launch.Need to get one of those launchers.

jlong34016

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What do you mean by hard to launch? I have a hard time with my 7.2 inch prop but i would expect a 9 inch at close to 20k to launch like a missle. I have the launcher but the shuttle will not fit between the engine and firewall.

Congrats on the 200 mph.

sydclement

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Hi Daryl:
Congrats on the 206.6/216 Whiplash.
If you have any questioms about the launcher
give me an e-mail.
It sure does make your launch alot smoother.
I have been using an APC 8.8-9.75 off the launcher.

Syd

Daryl Lane

Yes I would like to talk to you about the launcher, and would like to know how fast your plane it with that setup.

wingspan99

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So you're running a 7.5 pitch prop at about 29,000rpm for the 206mph run, and at about 30,000rpm for the 216mph run? Those are the rpm's required to see those speeds even theoretically, and with prop efficiency losses, it would take even higher rpms to reach those speeds in flight. Now maybe you're outrunning the prop in a dive, similar to the way the gliders can get above 226 mph just by pointing the nose down. But straight and level speed of 195mph still requires 27,500rpm to add up to the theoretical prop pitch speed, and higher rpms are required to overcome the prop slippage. Could you tach your engine for us and post your results? -Tom

ChuckAuger

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Don't muck up the works!

I haven't seen a single plane that would run the speed calculated, but they beat the heck out of it with a radar gun.

I'm like you, I figured the laws of physics would prevail, but I was sorely wrong. I don't know how this can be, but I really can't argue..everybody is doing it..so who am I to disagree??

BTW..the FAI doesn't allow radar for speed runs. There was a rocket powered car that broke the speed of sound ( Budweiser ) back in the '70's or '80's, but it was only timed with DOD radar one way and the record was disallowed.

There is obviously some effect that allows prop driven planes to far exceed the speed calculated by simple pitch X RPM readings. I just wish I could tap into this knowledge..

wingspan99

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I've been using prop pitch speed to estimate my speeds so I'm probably way underestimating. We know that prop pitch is measured at one point only on the prop, maybe the pitch near the root of the blade is becoming more effective at the higher rpms? This is very interesting, I'm going to have to get a radar gun for myself now. I've been using prop pitch speed to estimate my speeds so I'm probably way underestimating. -Tom

Troy-RCU

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The formulas for estimating pitch speed are just that, an estimate. You'd have to do a serious break down analysis of the whole set up including blade airfoils, twist distribution of the blade, in air RPMs, and of course airframe drag. The reason why you are able to go past this estimated pitch speed is because the formula only deals with blade angles, and the airfoils on the blades are creating lift. The faster you spin a prop, the higher the reynolds numbers, the more lift the blade produces. You also have aerodynamic unloading of the prop in air. It can increase quite a bit once up and zipping around.

jlong34016

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I believe the 45 jett can unload in the air to about 27,000 with the 7.5 pitch. I know my fai nelson will do that on the ground. This is really the only factor which allows the static rpm calculation to underestimate the airspeed. Someone here has an onboard tach for inflight use. Would like to see those numbers.

Daryl Lane

All I know is what we have tried. First prop was a 7.4-8 and it turned about 24000 on the ground, but never got on the pipe good,But in the air it hit two stages and run though the traps at 180.Then Paul and I tried a 8.75- 9.0, Then the Whiplash-JETT combo ran 206.0.Then we tried some larger props and had some trouble launching the plane. It was getting late in the day so we tried one more prop, it was a prop that Dan had ask me to try.The prop was a 9.0-7.5 and the speeds where 203.0,202,206.6,206.0 and as far as the rpms I do not know. But one thing I have learned in racing we do not race tach.

ChuckAuger

My Feedback: (12)

The trend on the Whiplash..people are getting faster speeds with larger diameter props..seems like the little props may not have enough thrust to go fast, even though they are spinning higher RPM.

I'm not doubting your readings or experiences, Daryl..just trying to get a handle on the whole equation. Thanks for throwing a few more numbers out there for me to mull over.