P85 - A New Aircraft

HomeBuiltAirplanes.com

Help Support HomeBuiltAirplanes.com:

Jeffd

Well-Known Member
Joined
Dec 15, 2011
Messages
115
Location
Overland Park, Kansas USA
Hi, Jeff!!! What a nice job you guys are doing!!!

Two questions:

a. what is the minimun powerplant requirement for the P85 (if possible, list hp/prop figures)?

b. fuselage lenght (prop spinner included) and wing spam?

Again, congrats...

Marcvini
Thanks for the nice words!

Minimum engine: I would say 350 HP as a minimum. The plane will certainly fly and perform "OK" on less power, but you would be wasting the airframe structural strength, as well as engine weight. Since the P85 is meant to use an LS engine, I can't imagine putting a decent LS engine together that would not make at least that much power. The engine currently bolted to the plane is a 402 cid stroker LS2 block with LS3 heads and intake. Dyno'd way over 400 hp at 5000 rpm (and even more at the 5400 peak HP rpm), but we are propping it to use about 380-400 hp out of the box.

Prop: On this first P85 we are using an 80 inch diameter, 3 blade prop. The 1.8:1 re-drive ratio results in 2800 prop rpm at 5000 engine rpm. Seems like a high helical tip speed at 5000 rpm, although Catto says it will work - I am sure he knows more about his props than I do. Entirely possible to use a higher numerical re-drive ratio with a larger diameter prop, up to 98 inches diameter will fit with adequate ground clearance.

Preliminary dimension:
Wing span 26.8 ft
Length 22.3 ft

Jeff
 

MARCVINI

Well-Known Member
Joined
Apr 16, 2014
Messages
295
Location
Pitanga/Paraná/Brazil
...Minimum engine: I would say 350 HP as a minimum.
Thanks for your ready reply. I wish you guys all success in your endeavour. You can be sure that auto V8 engines are the redeemers of experimental aviation.

Speaking of experimental aviation, I know that I may be entering the sacred territory of LSx engine conversions, but, if your preliminary drawings are proportionally correct, here is what an up right direct drive big block V8 would look like in your airplane:

P85 Big Block.jpg

It seems to me that 680 ftlb torque at 2700 rpm (for 350hp at 2700 rpm) is quite doable in an all aluminum bore and stroked big block V8. For the above sketch, I used the Ford 460 dimensions as reference. 34 inches is the length of the engine.

This is the dyno chart for the Chevy ZZ572:

Chevy Big Block Dyno.jpg

Those figures can be improved in a purpose built engine of the same size, such bumping compression ratio by one point, to reach 10,5:1 cr (more torque), dual plane intake manifold (at least 50 ftlb torque increase), purpose grind cam (more torque) and more stroke and less bore (the above engine has only 4.375 inch stroke and can be bumped up to 4.500/4.600 inch). So, there are lots of possibilities to achieve respectable torque at 2700 rpm in order to make your airplane fly decently.

Yes, I know that a geared LS engine has more power potential, but no one can deny the gains in terms of reliability and simplicity that an upright big block V8 spining at 2700 rpm has.

Food for thought...

Marcvini
 
Last edited:

Jeffd

Well-Known Member
Joined
Dec 15, 2011
Messages
115
Location
Overland Park, Kansas USA
Thanks for your ready reply. I wish you guys all success in your endeavour. You can be sure that auto V8 engines are the redeemers of experimental aviation.

Speaking of experimental aviation, I know that I may be entering the sacred territory of LSx engine conversions, but, if your preliminary drawings are proportionally correct, here is what an up right direct drive big block V8 would look like in your airplane:

View attachment 32846

It seems to me that 680 ftlb torque at 2700 rpm (for 350hp at 2700 rpm) is quite doable in an all aluminum bore and stroked big block V8. For the above sketch, I used the Ford 460 dimensions as reference. 34 inches is the length of the engine.

This is the dyno chart for the Chevy ZZ572:

View attachment 32847

Those figures can be improved in a purpose built engine of the same size, such bumping compression ratio by one point, to reach 10,5:1 cr (more torque), dual plane intake manifold (at least 50 ftlb torque increase), purpose grind cam (more torque) and more stroke and less bore (the above engine has only 4.375 inch stroke and can be bumped up to 4.500/4.600 inch). So, there are lots of possibilities to achieve respectable torque at 2700 rpm in order to make your airplane fly decently.

Yes, I know that a geared LS engine has more power potential, but no one can deny the gains in terms of reliability and simplicity that an upright big block V8 spining at 2700 rpm has.

Food for thought...

Marcvini
I like your enthusiasm - it is clear that you have spent time gathering/considering lots of V8 info, just as I have over the years. Why don't you purchase a P85 kit and install a big block direct drive package. We'll have fun and learn from the comparison of cost, weight and performance. It would be interesting to see the results.

Jeff
 

MARCVINI

Well-Known Member
Joined
Apr 16, 2014
Messages
295
Location
Pitanga/Paraná/Brazil
I like your enthusiasm - it is clear that you have spent time gathering/considering lots of V8 info, just as I have over the years. Why don't you purchase a P85 kit and install a big block direct drive package. We'll have fun and learn from the comparison of cost, weight and performance. It would be interesting to see the results.

Jeff
Well, I humbly have to admit that, as we say here in Brazil, I still have to eat lots of black beans to be capable of handling a machine like that of yours...

For now, my plans are way less ambitious: I am planing on building a direct drive inverted V8 powered Glasair Sportsman. I am leaning towards a Stroked (427= 4.000 bore X 4.250 stroke) SBF Windsor for the powerplant, mated to a CATTO FP propeller. Planing to start "cutting and welding" in 12 or 18 months, money permiting. More details at the "Direct Drive SBC" thread. Lots of interesting discussions there.

But life, till a certain extent, is unpredictable, so...

Marcvini
 

crytes

Well-Known Member
Joined
May 16, 2014
Messages
140
Location
Clarksville, TN / USA
This looks like a perfect fit. And compared to my idea of trying to design something prowler like but in composite much less headache. Are aiming for the same kit price as the rocket? And are the P85 and the radial rocket similar enough that one can be converted to the other? Did you have a projected burn rate to go with that theoretical top speed of 270 mph?
 

Jeffd

Well-Known Member
Joined
Dec 15, 2011
Messages
115
Location
Overland Park, Kansas USA
This looks like a perfect fit. And compared to my idea of trying to design something prowler like but in composite much less headache. Are aiming for the same kit price as the rocket? And are the P85 and the radial rocket similar enough that one can be converted to the other? Did you have a projected burn rate to go with that theoretical top speed of 270 mph?

P85 kit pricing is expected to be essentially the same as for the Radial Rocket. Yes you could convert from one to the other. Fuel burn at top speed? Figure about .50 lb/hp/hr.

Jeff
 

crytes

Well-Known Member
Joined
May 16, 2014
Messages
140
Location
Clarksville, TN / USA
Unless I'm doing something wrong at your minimum power number of 350 hp that Would come out to 29.1 gal/hour of avgas when going all out. If you get to 270 mph that comes to 9.3 mpg. 60% Would come to 162 mpg at 17.4 gph and i still get 9.3 mpg. I must be doing something wrong. Nearly 30 gal/hour don't sound right and i'm sure pulling back the power should save gas.
 

akwrencher

Well-Known Member
HBA Supporter
Joined
Oct 16, 2012
Messages
1,149
Location
Gustavus, AK
Perhaps it is possible to lean the engine more at cruise settings, getting a better BSFC? .5 is pretty rich.....
 

crytes

Well-Known Member
Joined
May 16, 2014
Messages
140
Location
Clarksville, TN / USA
I was looking at the rg and td pictures of the radial rocket and it got me to wondering. Will the cooling tunnel on the p85 accommodate the nose gear on the rg or will the p85 be a taildragger only?
 

Jeffd

Well-Known Member
Joined
Dec 15, 2011
Messages
115
Location
Overland Park, Kansas USA
Unless I'm doing something wrong at your minimum power number of 350 hp that Would come out to 29.1 gal/hour of avgas when going all out. If you get to 270 mph that comes to 9.3 mpg. 60% Would come to 162 mpg at 17.4 gph and i still get 9.3 mpg. I must be doing something wrong. Nearly 30 gal/hour don't sound right and i'm sure pulling back the power should save gas.

You has asked about fuel burn at top speed, so that is the question I addressed, based on dyne sheet fuel flow at full power, with air/fuel ratio at about 12.5. Power required vs speed is not linear, so mpg increases as speed decreases, to a certain point. Flight test will tell for sure, but based upon experience with the Radial Rocket I would expect the P85 to burn 8-10 gph at 200-220 mph true air speed, 12-14 gph at 240-250 mph tas, etc. Variables are altitude, lean setting fuel flows and such. As stated, flight testing will tell the story.

Jeff Ackland
Altitude Group LLC
About The Radial Rocket
 

Jeffd

Well-Known Member
Joined
Dec 15, 2011
Messages
115
Location
Overland Park, Kansas USA
I was looking at the rg and td pictures of the radial rocket and it got me to wondering. Will the cooling tunnel on the p85 accommodate the nose gear on the rg or will the p85 be a taildragger only?
Fixed gear taildragger is the gear configuration of choice for the P85 - the tricycle retract option would require radiator placement elsewhere. Retract tailwheel configuration is do-able, yet may still interfere with the radiator exit air cooling duct.

Jeff Ackland
Altitude Group LLC
About The Radial Rocket
 

Toobuilder

Well-Known Member
Log Member
Joined
Jan 19, 2010
Messages
4,601
Location
Mojave, Ca
Unless I'm doing something wrong at your minimum power number of 350 hp that Would come out to 29.1 gal/hour of avgas when going all out. If you get to 270 mph that comes to 9.3 mpg. 60% Would come to 162 mpg at 17.4 gph and i still get 9.3 mpg. I must be doing something wrong. Nearly 30 gal/hour don't sound right and i'm sure pulling back the power should save gas.
Seems perfectly reasonable. Doing the same math on my 260HP Rocket shows 21GPH - and that's exactly what my FF indicates on a full rich, sea level takeoff. At this power setting I think I can do about 230KTAS in level flight, yet at altitude and LOP I'm seeing 190KTAS at 10.5 GPH.

At 8500 feet the RV will do 165KTAS at 8.5GPH (19.4 MPG), but running all out gets me 177KTAS at a whopping 12.5GPH (14.1 MPG).

That's quite a spread, and shows that those last few knots are the expensive ones!
 

MARCVINI

Well-Known Member
Joined
Apr 16, 2014
Messages
295
Location
Pitanga/Paraná/Brazil
Jeff,

I believe that the airboat environment is much harsher that what one would find in an aircraft aplication. So, IMHO, I am quite sure that the PSRU you guys chose will work well.

Regardless of that, I believe that gear fretting (I hope it is the right name...) may become an issue during long periods without engine load on the gears, such as on descents.

So, is it something that requires major adressings in your prospective instalation or, given the way the PSRU was built, is it something not to be worried about?

Marcvini
 

MARCVINI

Well-Known Member
Joined
Apr 16, 2014
Messages
295
Location
Pitanga/Paraná/Brazil
Just for the fun of thinking about it. This dyno chart depicts the power of a beast, a Marine 632 Chevy Big Block:

632m_dynochart_575px.jpg

From Ohio Crankshaft , it is said to put out 900 ftlb torque at 3500 rpm, wich wouldn´t be too far from puting out 800 ftlb at 2800 rpm. Maybe some twicking could bring torque further north of 800 ftlb at 2800 rpm.

Well, in aluminum form, could be used direct drive, like this (I have already proposed it...):

P85 Big Block.jpg

Extravagant, expensive, but **** cool and quite feasible... If I win a lottery prize, you guys can count on me building it!!!

Marcvini
 

MARCVINI

Well-Known Member
Joined
Apr 16, 2014
Messages
295
Location
Pitanga/Paraná/Brazil
Wheel landing seems to be a nice alternative for the not very well initiated (me included...) in the art of landing taildraggers. That FP propeller seems to provide very nice clearance for using that landing technic in the P85.

So, what do you guys have to say about it? Any hint on the ground behavior of this airplane especially regarding landings?

Marcvini
 

crytes

Well-Known Member
Joined
May 16, 2014
Messages
140
Location
Clarksville, TN / USA
The radial rocket has pilot reports on it's webpage And i imagine most behaviors will be similar between the siblings I'd like to see a PSRU that would let you install a constant speed prop. But i want a coaxal prop too so I'm just hard to please.
 

MARCVINI

Well-Known Member
Joined
Apr 16, 2014
Messages
295
Location
Pitanga/Paraná/Brazil
The radial rocket has pilot reports on it's webpage And i imagine most behaviors will be similar between the siblings I'd like to see a PSRU that would let you install a constant speed prop. But i want a coaxal prop too so I'm just hard to please.
Well, I did my home work: wheel landing is recomended for the Rocket, so...

Loosing speed during aproaches may become a tad more dificult with the FP propeller. Any coments on that?

Marcvini
 

crytes

Well-Known Member
Joined
May 16, 2014
Messages
140
Location
Clarksville, TN / USA
Not sure but with higher compressions on liquid cooled engines I don't think the prop will spin the engine much when you pull off the power so that big prop probably still make an effective break.
 
2
Group Builder
Top