summerwind

i have a special application to which i need to use a sub plate between the engine mount and firewall.
i will be glad to go further into detail as to the model the engine is being used on, but only if asked

anyways, i would like to know what grade of aluminum is best or hardest, and at the same time light??
i need to make a disc out of this piece of aluminum that will incorporate a skid, and will be opened up to allow a passage for the venturi to breath.

MinnFlyer

My Feedback: (4)

You can use anything really, but I used to like using 6026 T-6

freakingfast

My Feedback: (3)

I'd use 7075 T6. (T6 indicates the temper, usually it's T-6) It's very strong and stiff. It's actually stronger than 1018 mild steel. The only drawback is that it is intolerant of bending, not ductile like the more commonly found 6061- T6, so on a high impact (crash) you may brake it, but that would be the least of your worries at that point. I love machining 7075, the chips fly, don't wad up in the cutter when you push the feed rates and has a great finish, many times this can offset the extra cost of it compared to other materials.

In any case, try to incorporate small radiuses on inside corners to stop cracking (stress risers).

freakingfast

My Feedback: (3)

If you plan on some bending, use the 6061. Thicker pieces can be bent with heat from an oxy acetylene torch but this may take out some temper.

airraptor

My Feedback: (66)

Summerwind. I think you should place that skid in another spot. I have flown many speed planes just using a wire skid. With the skid mounted on the fire wall the plane 90% of the time will bounce back up in the air and if the air speed is low you know what happens. I have found that having a skid come down from the bottom of the fus near the front of the wing. with a bend going toward the engine then a gental arc back toward the tail of the plane terminating about an inch or so behind the leading edge.

You can land the plane with it coming from the firewall area but have to fly it fast and fly it on the runway NOT land it. also smal lhin loop of wire on the wing tip will help with cartwheeling on the ground.

If you would like more thoughts or help shoot me an email with pics and i can help.

summerwind

hey thx for the input Minnflyer and FF
i knew it was either 6061 or 7075 but haven't messed with anything like this in some time.
i found both from suppliers on ebay for reasonable pricing. both have their purpose in my field.

summerwind

hi raptor,

i've been able to buy another 65 from Bill H.
man the guy knows his stuff and with a couple of his mods these engines are gonna be awesome to run.

PM me your email addy and i'll send you a couple pictures of what these are going in...........the skid has to be in it's planned location and hasn't presented a problem. once you see the model the engine is going in will explain a lot.
props have been tested and produce outrageous thrust, and are under transonic tip speeds.

freakingfast

My Feedback: (3)

I've been working on the same problem of near Mach tip speeds (.8-.9) and I think I have had an Eureka moment myself! (never would have believed it would work, unorthodox at first) Did the noise drop off radically on your prop too? What is your prop made of? Mine is Wood!

Broken Wings

My Feedback: (20)

If you just need a spacer/sub plate, I've used Delrin with good results. It's pretty tough. Taps well, easy to machine/cut. Lighter than aluminum...

I made this one for a Jett 90 with backplate mount and never had any issues.

summerwind

there seems to be a lot of fear and specualtion on Mach speeds of a prop, and rightly so, but what some people figure out to be proper tip speed of a prop for our small racing engines is actually less than the true number.
for example, the formula used for tip speed would have a 10" prop being exceeded at 23,000 rpm. but in reallity we used props this size at over 24,000 rpm with no side effects or disaster as the pencil pushers would have us believe.
while my use of the OPS .65 is not RC related, it is used in competition where every last useable rpm is extracted thru proper prop diameter and pitch. we never use any racing engine with consideration to tip speed being a problem because we just don't hit the disaster zone.

props i use are made in molds that were made for us by Doug Galbreath who is a noted world class Free Flight flyer amongst other noteable achievements. when laying up a run, i try different packings to find the formula that lets the tips washout under speed to achieve max unload in the air...........each layup is numbered and a second packing is set aside for future molding once the right prop proves itself.
never have lost a prop blade no matter how fast the prop is turned while testing.

controlliner

7075 T6, That is the strongest and lightest alloy I use on aircraft repairs (full scale military)

freakingfast

My Feedback: (3)

If you are making good thrust above that point....there is little doubt you have the correct profile at the tips,

vicman

My Feedback: (10)

I'll third using 7075. 7068 if you have any, that's what I made mine out of. It's a little harder to find but much stronger.

summerwind

really appreciate all the input guys..............the models i fly are built with a gram scale used throughout the process so i'll machine the parts from both grades. have the 6061 in hand, but still waiting for the 7075.

it'll be a while, but i will post results when the model is done