Randy Smith

Another thread was referring to the unpublished Q40 carbon fiber prop rule. Thought I would post it here.

While I was in Phoenix at the JR Gold Cup, I spoke with Barry Leavengood and asked him for the precise wording of the cf prop rule for the Q40 event. Barry received the wording in an email from Steve Kaluf, Technical Director of the AMA. Barry gave me a hard copy of the rule at the field. I have typed the hard copy out in this email below.

When in doubt always refer to the official AMA Competition rulebook.

Randy Smith
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16.1 Event 422 Q40
16.1.2 Powerplant
16.1.2 b Propeller

1) Material: Either wood or a chopped carbon fiber filled injection-molded compound with tensile strength at least equivalent to that of Ticona Celstran PA6-CF35-15.

2) Dimensions: No limit for wood. Injection-molded propellers shall have a diameter, pitch, blade width, and blade airfoil identical to that of the approved part number at every measurable station.

3) Availability, modification: Wood propellers may be modified. Injection-molded propellers shall be commercially available and stock except for balancing, etc. as permitted by paragraph 7.5.2 under "General Model Aircraft Requirements".

4) Prior approval: APC part number LP07480C, bearing raised markings "7.4 x 8" on the blade outside the hub, is approved.

5) Eligibility for competition: A propeller once approved shall be eligible for competition so long as it remains commercially available, as defined in section 2, "Defined Terms".


Submitted by: Mike Condon AMA 71839

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General Model Aircraft Requirements
7.5.2. In events requiring stock, commercially available propellers, the following modifications may be made without penalty:

(a) One blade may be sanded on the top (front) side only for balancing.

(b) One side of the hub may be sanded for balancing.

(c) The shaft hole may be enlarged, but only as much as necessary to fit the engine crankshaft.

The enlarged hole shall be concentric with the original hole.

(d) Edges and tips may be sanded, but only as much as necessary to remove sharp molding flash.

PylonWorld

Thanks Randy.

If I could get Mr. Burgdorf to produce a CF Q-500 prop, I would be in business with a Q-500 engine, if I could get the prop approved.

Otherwise, I'll have to find some wood Q-500 props.

The main reason I wanted to go bigger on the diameter was because of the nose design of the H-1. After getting one half of the plug done, I don't think the cowl will be a big problem. But I won't know until I produce an H-1 and fly it.

luv to race

My Feedback: (1)

I'm lost ? What would be the purpose of a CF Q500 prop, when concerning a Q40 design? A Q40 motor won't even come close to turning a Q500 prop.. unless it had 5 pitch or so...

Randy B.

PylonWorld

Because of the frontal area of the simulated radial cowl on the H-1, it may be best to run a larger diameter prop. You wouldn't want to run a larger prop unless you could reduce the pitch ... or you could run a larger prop at a higher pitch on a Q-500 engine at reduced RPM's and the pitch speed would be comparable to a Q-40 with a 7.4 x 8, and you would have a larger propulsion area.

Kurt Bozarth flew a Kangke F3D/30 with a Nelson Q-500 in it competitively against some Q-40's ... So, the idea of running a Q-500 engine with a 8.8 x 9.25 on it in Q-40 is not completely preposterous. The problem is that it would not be legal to do so, at least with an APC Q-500 prop.

I'm not sure the frontal area on the Hughes H-1 I'm doing will be a problem. But it certainly may prove to be a problem. In which case, the plane should make a nice Q-40 legal semi-scale sport racer.

bl10

Back when there was a lot of noise being made about slowing down both 422 and 428 one of the proposals for Q40 was using Q500 props. A couple of us tried this to see what the effect was. We kind of figured the Q500 prop / sleeve combo would result in quicker 1st lap times then slower laps and lower top end speed. To our surprise the first lap was slower as was every other lap. Not only could we not get times close to Q40 we couldn't even get competitive Q500 times. We didn't try a bunch of different combinations but as I recall the best we got out of the Q40 was a 107 while the Q500 went 105 with the same engine. The Q40 was a good Vendetta and promptly went 103 with a Q40 engine and prop. Probably the much higher wing loading of the Q40 was hurting it. There have also been attempts to use Q40 timed engines on Q500 airframes using a low pitch prop (wood because the APC gray props are not stressed for the RPM required by the Q40 engine) . All the attempts I am aware of were failures probably due to the small pitch and increased prop drag.



Barry

PylonWorld

Thanks for the info Barry.

I guess I'll just have to finish the H-1 up and see how it does.

Thanks so much for all of the info and help you have provided to me through a variety of communication mediums. I truly appreciate the time and effort you have put into helping me with various techniques and concepts.

rvanbare

Randy and Barry,

I made mention to Jim Allen at Phoenix that APC had produced another CF propellor with a different designation than 7.4 X 8". The justification for the new mold was to clean up flashings etc. The new propellor is marked as 7.4 X 8.0" not 7.4 X 8". Where in the rule does it state that the propellor can be changed to clean up the flashings? Not to mention that the new propellor turns about 500 to 700 RPM less. I wonder why it turns less. Can it be a different propellor? Go figure.

The only propellor approved is the 7.4 X 8", not 7.4 X 8.0".

Let's follow the rules so we do not have speed creep. It will happen or just let all carbon props people want to make be approved.

Rusty Van Baren

luv to race

My Feedback: (1)

Rusty,

Go to NMPRA.ORG and read the 422 Prop Rule stuff in there. I think you'll find some info on which prop is legal "per the rules"..

Randy B.

Randy Smith

Rusty,
I believe what happened was Fred's mold had produced so many props that it was in need of maintenance. ie. molding flash had developed and he wanted to clean this up as a matter of good manufacturing practice and to produce a quality product. Had he left the pitch designation markings in the mold alone, none of us would be having this discussion.

I'm sure all sorts of prop manufacturers modify their tools from time to time to maintain quality. The end result is generally transparent to the customers. In this case, the new pitch designation has given the perception that the 8 and 8.0 props are different even though they are sold under the same product number.

Personally, I think it's reasonable to expect some change in static rpm measurements after a mold change (even just to clean up flash). Given time, all the '8' props will work their way through the inventory pipe and we'll all be running 8.0 eventually.

I'll say it again.... we all know that a few hundred rpm is not going to win or lose a race. The guy who makes 30 consistent corners in every round is the guy who wins. Those that choose to run carbon should bolt on a prop (8 or 8.0) and go fly.


Randy S.

daven

My Feedback: (1)

Maybe its just me, but I would think that if you cleaned up the mold and flashing, the prop would turn up more. It seems that the cleaned up props are actually slower.

I would also disagree that a couple hundred rpms don't matter. If two people make the same exact 30 perfect turns, the one with the extra rpms will have won the race.

rvanbare

I believe the rule states the propellor bearing the marking of 7.2 by 8 is the rule. I didn't see any place where it said 7.2 X 8.0.

Point out the exact section and paragraph if I am mistaken. The rule did not mention anything about flashing etc. I did not say it had to be the best prop it said it had to be the prop marked 7.2 X 8 .

Personally I would like to have some more of the 7.2 X 8 props.

Randy S. if you want to give up 3-500 rpm go for it but I don't . I don't feel you can give up anything in todays competition. Somebody will have the extra RPM and put it on the course for 10 laps.

Rusty

PylonWorld

This part of the rule is particularly important because of the first two words:

4) Prior approval: APC part number LP07480C, bearing raised markings "7.4 x 8" on the blade outside the hub, is approved.

In my opinion, that means the particular prop is approved. The rest of the rule verbage does not preclude the approval of other props, as long as they meet the other parts of the rule. However, IANAL, and I am a rookie ( at best ).

Randy Smith

Rusty,
Yup, and I suppose that's why I'm not winning the JR Gold Cups.
Damn! I knew I was doing something wrong.


See you at the races (some where in the middle of the pack)



Randy S

luv to race

My Feedback: (1)

A rule is a rule. That's the bottom line. Something has to be changed. The prop? The rule? doesn't matter to me either way. Without these specific rules, we have nothing but chaos.....

RB

rvanbare

RB

That is my point exactly. All I ask is "just follow the rule" nothing more or nothing less.

If you start letting it, what seems to be a small issue of a different marking slip through , then we might as well just open the cf prop rule to all cf propsincluding different manufacturers.

I can give you a number of reasons why the prop designation may be slightly different from a manufacturing perspective, but I don't think this is the place to air those concerns.

Simply solution: Follow the rules or change them CD's.

Rusty

PylonWorld

Rusty,

Since the 7.4 x 8 is no longer commercially available (which "by the rules" makes it illegal), without a new prop approval, the days of the CF prop would be over.

What is your proposed solution?

rvanbare

Don,

Now that is an interesting thought. I suppose you could look at it that way. I hadn't looked at it that way, but you could say we do not have an approved cf prop.

Rusty

rvanbare

Don,

Quick solution for APC is dig out the original mold and make the prop with 7.4 X 8 designation. Now you have a legal prop.

Rusty

DrewTelford

Well, we can touch one blade to 'balance' it, so if we remove the .0 ..........


dt

js3

My Feedback: (3)

Hopefully, the blade with the "0" on it is the heavy blade

Don't you just love messes like this?

I didn't like this rule to begin with.