Minimum power for a 9# plane
06-27-2012, 02:32 AM
#1
Senior Member
Thread Starter
Minimum power for a 9# plane
I do not want to restart the overpower controversy, but...
I know manufacturers always recommend under-powered engines to minimize their claims. However, I was told picking the high end engine should be OK. Not with my H9 Spitfire 60. Hangar 9 recommends 60 to 75. The plane is about 9# and I have an OS75AX running a 13-7 prop but the plane is still very underpowered. Should I change theprop? I have followed the instruction of brake-in with 2 tanks, and have made about 6 flights with the engine, so I assume it’s fully broken in.
Thanks,
I know manufacturers always recommend under-powered engines to minimize their claims. However, I was told picking the high end engine should be OK. Not with my H9 Spitfire 60. Hangar 9 recommends 60 to 75. The plane is about 9# and I have an OS75AX running a 13-7 prop but the plane is still very underpowered. Should I change theprop? I have followed the instruction of brake-in with 2 tanks, and have made about 6 flights with the engine, so I assume it’s fully broken in.
Thanks,
06-27-2012, 07:33 AM
#2
My Feedback: (-1)
RE: Minimum power for a 9# plane
Yes, with any new plane, even if I use one of my trusty old engines one of the first things I do is take a fist full of props that are in the range of my engine and start testing props to locate the prop that will fly the plane/engine combo I have the way I want it to. Prop testing is why and how most of us end up with a wall full of props like John Bckner. {{Please show a photo Jhn
}} I no longer have a box full of props like I used to, I have given way too many away out at the field. I'm going to try to stock pile again this year when I go to some swap meets again. Last one My WIFE was with me so I passed up a lot of good deals that I really needed!!
Truth, no bull and there were a few carbon fiber in the correct size and price!!
}} I no longer have a box full of props like I used to, I have given way too many away out at the field. I'm going to try to stock pile again this year when I go to some swap meets again. Last one My WIFE was with me so I passed up a lot of good deals that I really needed!! Truth, no bull and there were a few carbon fiber in the correct size and price!!
06-27-2012, 12:49 PM
#6
RE: Minimum power for a 9# plane
Problem with that is I am not a dealer I am a consumer and don,t sell. Ya see us Gimpy guys tend to live our lives in in drive thru's. And the thought of having to saddle up and go anywhere except the flying field is quite painful. So stocking up is a really simple solution.
Heck use to have to go to Lake Havasu to a retail store and eveytime I would go I called and an hour later would pull up to just outside the office and honk, in minutes I was loaded up in my chair and ready to shop. Hows that for service. Well unfortunately they finally closed their doors for some years.
It was back to the UPS man (Ick) and maybe one or two trips a year to Las Vegas (better than two hours. But walla we now have a retail store once agine and I trained the fellow (flying and what we needed). He's doing great in both (just acheved his first jet flights at a nearby dry lake). And he delivers.
Mark just for giggles try an APC 12/7 to unload your engine just a bit and perhaps pick up one or two mph. That small diff just may present an entirely different feel and perhaps something you may like.
The real point is I suppose don,t be afraid to experiment. Whats fine for one persons type of use and another may be different.
John
Heck use to have to go to Lake Havasu to a retail store and eveytime I would go I called and an hour later would pull up to just outside the office and honk, in minutes I was loaded up in my chair and ready to shop. Hows that for service. Well unfortunately they finally closed their doors for some years.
It was back to the UPS man (Ick) and maybe one or two trips a year to Las Vegas (better than two hours. But walla we now have a retail store once agine and I trained the fellow (flying and what we needed). He's doing great in both (just acheved his first jet flights at a nearby dry lake). And he delivers.
Mark just for giggles try an APC 12/7 to unload your engine just a bit and perhaps pick up one or two mph. That small diff just may present an entirely different feel and perhaps something you may like.
The real point is I suppose don,t be afraid to experiment. Whats fine for one persons type of use and another may be different.
John
06-27-2012, 01:11 PM
#7
Senior Member
RE: Minimum power for a 9# plane
GB & JB - when you stock up are you using a specific brand of prop? Or would you cross manufacturers within the same prop size (APC 12x8 and a Zinger 12x8)?
06-27-2012, 06:06 PM
#8
My Feedback: (-1)
RE: Minimum power for a 9# plane
Different types, but most the time I end up using APCs with my glow engines and Xoars on my gas engines. If I find a deal on some good props like carbon fiber I will pick them up.
John, Nice Twice sold and it isn't so nice right now. Not much in the way of stock on hand. I hope they will get better. They also moved around the corner? Easier to find but not the room Denney had!
John, Nice Twice sold and it isn't so nice right now. Not much in the way of stock on hand. I hope they will get better. They also moved around the corner? Easier to find but not the room Denney had!
06-27-2012, 09:10 PM
#9
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RE: Minimum power for a 9# plane
I'm not sure about that particular plane, but kit manufacturers are notorious about recommending engines that are under powered for their planes. A nine pound plane, especially a warbird, just seems to beg for an engine more powerful than a .75 two stroke.
Gene, have you tried MAS scimitar props? I know APC props are probably the best performing, but they are so damned ugly and look like something somebody would bring to a knife fight. MAS scimitars don't look quite as bad but I have not bought any. A 13-7 on a .75 sounds about right but if the plane is underpowered, the OP might want to experiment with something in the 12-5 to 12-8 range. Might gain a few RPM at any given throttle setting.
Gene, have you tried MAS scimitar props? I know APC props are probably the best performing, but they are so damned ugly and look like something somebody would bring to a knife fight. MAS scimitars don't look quite as bad but I have not bought any. A 13-7 on a .75 sounds about right but if the plane is underpowered, the OP might want to experiment with something in the 12-5 to 12-8 range. Might gain a few RPM at any given throttle setting.
06-27-2012, 09:33 PM
#10
Moderator
RE: Minimum power for a 9# plane
What RPM are you getting? If you're topping out at 12k you're not getting into the engines power band. 14k on the ground is more like it and will unload to a good bit more in flight.
06-28-2012, 07:58 AM
#12
My Feedback: (-1)
RE: Minimum power for a 9# plane
Pop, that was my morning laugh. Yes I have tried the scimitars but only the small ones for .46 engines. They looked so much better on my WWII Bipes during my Bipe years in the hobby. I never did do a comparison test with them though so I don't know how they compare with an APC. Once I start an engine I can't see the prop anyway.
One thing I used to do with the APCs. After I built a new plane, did the maiden and trim flights and all the prop testing I would go and buy several props for the new plane in the size I liked. I would ream, balance then mix up a nice hot batch of Ritt Dye and soak the new props until they got to the color I was looking for.
I had people at the IMAA air shows convinced I had them custom made for my planes by a guy and I could get them for people at some really stupid price. I could have sold hundreds of them!! YES, I did tell people how I did it, I'm a butt head but not a complete butt head!!
John, the new shop will break your hart!![:-]
One thing I used to do with the APCs. After I built a new plane, did the maiden and trim flights and all the prop testing I would go and buy several props for the new plane in the size I liked. I would ream, balance then mix up a nice hot batch of Ritt Dye and soak the new props until they got to the color I was looking for.
I had people at the IMAA air shows convinced I had them custom made for my planes by a guy and I could get them for people at some really stupid price. I could have sold hundreds of them!! YES, I did tell people how I did it, I'm a butt head but not a complete butt head!!
John, the new shop will break your hart!![:-]
06-28-2012, 08:19 AM
#13
RE: Minimum power for a 9# plane
I ran a 13x5 on my 55AX. Sounds like you're under propped. You can also try fuel with more nitro content.
Personally 12000 revs sounds food to me, bigger engines spin slower. 12000-13000 is good for a 46AX. 10000 on a 1.20AX.
APC will give you the most thrust. EMP is a decent cheap prop and it is black. I would also run a Coat woodie. NOT a Turnigy, they are unfinished pieces of junk.
Personally 12000 revs sounds food to me, bigger engines spin slower. 12000-13000 is good for a 46AX. 10000 on a 1.20AX.
APC will give you the most thrust. EMP is a decent cheap prop and it is black. I would also run a Coat woodie. NOT a Turnigy, they are unfinished pieces of junk.
06-28-2012, 08:51 AM
#15
My Feedback: (-1)
RE: Minimum power for a 9# plane
ORIGINAL: gaRCfield
Oh yeah, answer to the real question: I have two 9# planes. They had 1.20AX motor, or YS 1.10, for good to great Aerobatic performance. A .90 is probably good for your plane.
Try a 14x7 and 30% fuel, and a 'hot' glow plug.
Oh yeah, answer to the real question: I have two 9# planes. They had 1.20AX motor, or YS 1.10, for good to great Aerobatic performance. A .90 is probably good for your plane.
Try a 14x7 and 30% fuel, and a 'hot' glow plug.
What motor would you use in a 9 pound war bird with a real high wing loading. Maybe something like a SpitFire?
06-28-2012, 09:04 AM
#16
Senior Member
Thread Starter
RE: Minimum power for a 9# plane
I don't get it. I am now running a 13-7 prop on my 75.
I find the mix very under power with my 9# plane.
I do appreciate all the input, but how come some suggest I go up to a 14-7 and some 12-8
Do I need more torque or do I need more speed for that plane?
So, should I increase the diameter or decrease it?
I find the mix very under power with my 9# plane.
I do appreciate all the input, but how come some suggest I go up to a 14-7 and some 12-8
Do I need more torque or do I need more speed for that plane?
So, should I increase the diameter or decrease it?
06-28-2012, 10:09 AM
#18
My Feedback: (551)
RE: Minimum power for a 9# plane
ORIGINAL: markhamregular
I don't get it. I am now running a 13-7 prop on my 75.
I find the mix very under power with my 9# plane.
I do appreciate all the input, but how come some suggest I go up to a 14-7 and some 12-8
Do I need more torque or do I need more speed for that plane?
So, should I increase the diameter or decrease it?
I don't get it. I am now running a 13-7 prop on my 75.
I find the mix very under power with my 9# plane.
I do appreciate all the input, but how come some suggest I go up to a 14-7 and some 12-8
Do I need more torque or do I need more speed for that plane?
So, should I increase the diameter or decrease it?
Are you running it off peak power? Lean the needle to peak rpm and then back in down 200. Hold the nose straight up at full throttle. If the engine doesn't lose rpm, you are ready to fly.
The problem could be the wrong prop. 13x7 is actually a little oversized for a 75. (OS sells a lot of engines in Europe and Japan where noise is a very serious problem, and they recommend oversize props to keep the noise down.) If your airplane is too slow, go for a prop with less diameter. Like 12x7. If the speed is OK but takeoff and climb performance is lacking, go for less pitch. Like 13x5. You should be looking for 11-12,000 on the ground.
Or you could put a 91 in it.
Jim
06-28-2012, 10:35 AM
#19
Senior Member
Thread Starter
RE: Minimum power for a 9# plane
Jim,
I am going to try your suggestion and buy today an APC 12-7 and 13-5.
As for the 90, they are not free. I have another 75 without a home.
If I can sell my 2 OS75, I will definetly go for a 95.
Thanks
I am going to try your suggestion and buy today an APC 12-7 and 13-5.
As for the 90, they are not free. I have another 75 without a home.
If I can sell my 2 OS75, I will definetly go for a 95.
Thanks
06-28-2012, 10:50 AM
#20
RE: Minimum power for a 9# plane
I am not an expert like these guys, but a modern .75 c.i. for a 9 lb warbird is not too unreasonable to fly scale, but not 3D.
I would start carefully tuning the engine. Then the prop size. Then, consider the muffler you are using. Is it too restrictive? Do you have leeway on what muffler you can use? Maybe not on a warbird. I would leave the engine swap to last choice since it is costly and more work. You will still have to experiment with props after the engine swap anyway.
I would start carefully tuning the engine. Then the prop size. Then, consider the muffler you are using. Is it too restrictive? Do you have leeway on what muffler you can use? Maybe not on a warbird. I would leave the engine swap to last choice since it is costly and more work. You will still have to experiment with props after the engine swap anyway.
06-28-2012, 11:15 AM
#21
RE: Minimum power for a 9# plane
The 46 can turn a 12X5 at 12000. The 55 turns a 12x7 nicely (in my Venus 40).
A 9# warbird with a high wing loading? I would look at a something between a 1.10 and a 1.50 4-stroke, (hmm, saito 1.50 is nice and light!) Or the 120Ax.
Electric is sweet. If I soil my work clothes flying, its probably my thumbs and not the fuel.
A 9# warbird with a high wing loading? I would look at a something between a 1.10 and a 1.50 4-stroke, (hmm, saito 1.50 is nice and light!) Or the 120Ax.
Electric is sweet. If I soil my work clothes flying, its probably my thumbs and not the fuel.
06-28-2012, 02:22 PM
#22
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RE: Minimum power for a 9# plane
I recently assembled a "Great Planes Giant Big Stick" and the comment in there instruction manual is that it is better to have the plane slightly overpowered than under powered (you don't have to have the throttle wide open). I mention this as it slightly surprised me usually manufacturers recommend a slightly smaller engine I believe.
06-28-2012, 05:04 PM
#23
My Feedback: (-1)
RE: Minimum power for a 9# plane
A longer prop with a smaller pitch will give you a slower plane with more torque and a shorter prop with a bigger pitch will give you a faster top speed with less torque. Saying that makes it easy to understand. Now it is up to the pilot to start testing different props to make the plane fly the way the pilot likes the plane to fly. As a pilot I like a plane with as much torque to give me the most vertical as I can get from my plane/engine combo. I don't care about the speed very much. Old school pattern pilots used to want as much speed as they could get to pull the vertical movements because the planes were limited to engine size.
No one knows what you are looking for in your Spit? Really fast or something with some torque to pull the plane on an up line better. If you say both then you may want a bigger engine under the hood? It's all pilots choice. Understanding this in advance is a lot of help when deciding on an engine for a new plane. For your plane I would have made a different choice but I already have a couple of the engines Would have chosen so I wouldn't have had to spend any more money. Money is another factor in this choice.
No one knows what you are looking for in your Spit? Really fast or something with some torque to pull the plane on an up line better. If you say both then you may want a bigger engine under the hood? It's all pilots choice. Understanding this in advance is a lot of help when deciding on an engine for a new plane. For your plane I would have made a different choice but I already have a couple of the engines Would have chosen so I wouldn't have had to spend any more money. Money is another factor in this choice.
06-28-2012, 06:58 PM
#24
RE: Minimum power for a 9# plane
ORIGINAL: JohnBuckner
Problem with that is I am not a dealer I am a consumer and don,t sell. Ya see us Gimpy guys tend to live our lives in in drive thru's. And the thought of having to saddle up and go anywhere except the flying field is quite painful. So stocking up is a really simple solution.
Heck use to have to go to Lake Havasu to a retail store and eveytime I would go I called and an hour later would pull up to just outside the office and honk, in minutes I was loaded up in my chair and ready to shop. Hows that for service. Well unfortunately they finally closed their doors for some years.
It was back to the UPS man (Ick) and maybe one or two trips a year to Las Vegas (better than two hours. But walla we now have a retail store once agine and I trained the fellow (flying and what we needed). He's doing great in both (just acheved his first jet flights at a nearby dry lake). And he delivers.
Mark just for giggles try an APC 12/7 to unload your engine just a bit and perhaps pick up one or two mph. That small diff just may present an entirely different feel and perhaps something you may like.
The real point is I suppose don,t be afraid to experiment. Whats fine for one persons type of use and another may be different.
John
Problem with that is I am not a dealer I am a consumer and don,t sell. Ya see us Gimpy guys tend to live our lives in in drive thru's. And the thought of having to saddle up and go anywhere except the flying field is quite painful. So stocking up is a really simple solution.
Heck use to have to go to Lake Havasu to a retail store and eveytime I would go I called and an hour later would pull up to just outside the office and honk, in minutes I was loaded up in my chair and ready to shop. Hows that for service. Well unfortunately they finally closed their doors for some years.
It was back to the UPS man (Ick) and maybe one or two trips a year to Las Vegas (better than two hours. But walla we now have a retail store once agine and I trained the fellow (flying and what we needed). He's doing great in both (just acheved his first jet flights at a nearby dry lake). And he delivers.
Mark just for giggles try an APC 12/7 to unload your engine just a bit and perhaps pick up one or two mph. That small diff just may present an entirely different feel and perhaps something you may like.
The real point is I suppose don,t be afraid to experiment. Whats fine for one persons type of use and another may be different.
John
06-28-2012, 07:00 PM
#25
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RE: Minimum power for a 9# plane
I fly the H9 Spitfire wtih a Saito 100 and an MA 14-8 K-series prop. 20/20 fuel at 5000 ft field altutude. This set up provides plenty of power of any kind of scale flight. I'm not a big fan of MA but they look much better than APC on the warbirds.
Greg
Greg