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Slow (relative) 7A

7

7DeltaLima

Well Known Member
OK, I admit it. I seem to have a slow 7A relative to what I see others post as their numbers.

I'm flying a 7A with about 310 hours running a IO360-A1B6 (dual mags) swinging a 3 blade MT prop. The plane flys like a dream, always has. Smooth as can be. Doesn't have a heavy wing, ball centered, flys hands off. My point, the plane appears to be built straight.

I went out one last time tonight and did one more run just hopeing that a miracle had happened and I'd gained 10 knts. :) before confessing I'm slow. :D

My numbers tonight and they are consistant with past runs:

trk 90 - gps 169 kts
trk 360 - gps 146 kts
trk 270 - gps 167 kts
trk 180 - gps 192 kts

which using GPS spreadsheet yields 169.3 knots avg speed with .3 std dev. I see others consistently posting above 180 kts avg.,

RPM 2650 MP 24.5 WOT Den Alt 8000 leaned to best power ~13 gph Ind Alt 6810 & baro 29.98 1140lbs empty + 230 me + ~30gal fuel

I've read the posts about the MT 3 blade being 3-5 knts slower and I'd probably trade that for the smoothness.

My questions.... where do I start to try to improve the speeds - what/how do I check. Is it possible/probable it's mostly attributable to the 3 blade prop? What else should I look at? If the fairings were mis-aligned, wouldn't it be indicated by the plane not flying straight? I know there are other RV's running the 3 blade MT, what kind of numbers are you seeing in real life?

Thanks for any suggestions.
Doug
 
How well aligned are the flaps and ailerons with the wing? Is it possible that they could be angled a bit down?

Where does the leading edge of the elevator counterweight sit with respect to the HS when at max cruise? (I'm looking for a symptom of misrigged flaps or ailerons).

What is the height of your inlets in the cowling, measured at the aft end of the fibreglas? If you have margin in your cooling, try making a temporary reduction in size of the cowl inlet to see the effect.

What do you have for external antennae?

Did you fly the aircraft without fairings, get the rigging sorted out, then add fairings incrementally? Or did you have all fairings on from the start? If the latter, maybe you have some fairings misrigged in one direction, and the tendency is cancelled out by other fairings misrigged in the other direction.

What is the rate of climb at VY? Measure the rate of climb with a stop watch against the altimeter - don't use the VSI. Describe the altitude and temperature at which you did this test. I'm looking for a way to confirm the engine isn't down on power.

Have you calibrated your tachometer? How does the MP gauge compare to the actual barometric pressure on the ground (not the altimeter setting)?

Have another builder inspect the aircraft, looking for anything unusual that could increase drag.
 
7DeltaLima said:
RPM 2650 MP 24.5 WOT Den Alt 8000 leaned to best power ~13 gph Ind Alt 6810 & baro 29.98 1140lbs empty + 230 me + ~30gal fuel
Click to expand...
"Best power" is always an ambiguous thing when anybody other than Walter Atkinson mentions it. :rolleyes: Simple solution...try leaning to peak indicated airspeed. It may not recover all the speed you want, but it probably will produce another 1-2 knots. Also, close your vents.
 
Also check your timing and make sure it's where you want it. I believe on your engine, stock timing is 20 BTDC.
 
More data

Kevin, 1st thanks for the questions as they provide a place to start.

How well aligned are the flaps and ailerons with the wing? Is it possible that they could be angled a bit down?
Click to expand...

Flying straight and level the left aileron is down below the wing tip what appears to be ~1/2 inch when viewed from the left seat. The right aileron is up correspondingly. I've always assumed this was just wing tip mis-alignment but sounds like this may be the place to start.

Where does the leading edge of the elevator counterweight sit with respect to the HS when at max cruise? (I'm looking for a symptom of misrigged flaps or ailerons).
Click to expand...

Don't know. I'll need to verify.

What is the height of your inlets in the cowling, measured at the aft end of the fibreglas? If you have margin in your cooling, try making a temporary reduction in size of the cowl inlet to see the effect.
Click to expand...
I don't have much cooling margin with the A1B6 so this would be one of the last places to work on but will review.

What do you have for external antennae?
Click to expand...
One bent whip and one stub for transponder on the belly. Archer in the wingtip for Nav.

Did you fly the aircraft without fairings, get the rigging sorted out, then add fairings incrementally? Or did you have all fairings on from the start? If the latter, maybe you have some fairings misrigged in one direction, and the tendency is cancelled out by other fairings misrigged in the other direction.
Click to expand...
I first flew with no fairings. After about 10-12 hours I added gear leg fairings to help with cooling and finally added the wheel pants after 20-30 hours. Nothing really stands out as a problem in doing so. In hindsight, what I don't know though is if the ailerons aligned with the wing tips without any fairings.???


What is the rate of climb at VY? Measure the rate of climb with a stop watch against the altimeter - don't use the VSI. Describe the altitude and temperature at which you did this test. I'm looking for a way to confirm the engine isn't down on power.
Click to expand...
I can't lay my hands on recent data but here is a data point from initial tests when the plane had ~12 hours on it. The plane had gear leg fairings on the mains, no wheel pants and nothing on the nose leg.

110 kias starting below 2000, timer started passing through 2000.
2-3000 :32
3-4000 1:06
4-5000 1:48

95 Kias
2-3000 :29
3-4000 :58
4-5000 1:33

85 kias
2500 - 3500 :30
35-4500 1:03
45-5500 1:37
55-6500 2:16
65-7500 2:56




Have you calibrated your tachometer? How does the MP gauge compare to the actual barometric pressure on the ground (not the altimeter setting)?
Click to expand...
I just verified the tach. I had the prop dynamically balanced (didn't do much with the MT as it was very good to start with) Tuesday and the Tach is accurate. Can't specifically say MP vs baro but I believe I'm seeing >28 mp on takeoff.

Have another builder inspect the aircraft, looking for anything unusual that could increase drag.[/QUOTE]

Thanks again for taking the time to respond. Looks like I need to investigate the aileron to wing tip as the first step.

Doug 7A
~310 hours
 
Best Power

dan said:
"Best power" is always an ambiguous thing when anybody other than Walter Atkinson mentions it. :rolleyes: Simple solution...try leaning to peak indicated airspeed. It may not recover all the speed you want, but it probably will produce another 1-2 knots. Also, close your vents.
Click to expand...


Dan, that's actually what I did for best power. I'd read a previous post or somewhere on your site to do that. I leveled off, got everything trimmed, hit AP for heading and alt then spent a few minutes tweaking the mixture using airspeed as metric. Didn't close the vents though.

Thanks,
Doug 7A
 
Cooling baffling/Aileron adjustment

Check this as well as this is the one place you can get a lot of extra drag if you have leaks. Also make sure you have glassed in the inlet ducts on the top of the cowling. When they are first installed, there is a pass thru between the inside of the duct and the outside of the cowling which is a serious leak. By glassing these openings closed it helps with speed and cooling.

Also, I noted something strange when setting my ailerons. Be sure your elevator is clamped neutral before adjusting ailerons to center. If you watch your ailerons when you move the stick fore and aft, the ailerons actually move up/down a little! If you set your ailerons with the elevator UP or DOWN, they won't be the same at neutral. Just an observation.

Good luck!

BTW, my -7A with Superior 0-360 180 hp, carbed, mags, Hartzell blended airfoil prop and unpainted with all intersection fairings and pants trues about 179 - 180 kts (WOT and 2650 rpm). My ailerons are perfectly straight in level cruise as well as the elevator counterweights in relation to the HS.
 
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7DeltaLima said:
110 kias starting below 2000, timer started passing through 2000.
2-3000 :32
3-4000 1:06
4-5000 1:48

95 Kias
2-3000 :29
3-4000 :58
4-5000 1:33

85 kias
2500 - 3500 :30
35-4500 1:03
45-5500 1:37
55-6500 2:16
65-7500 2:56
Click to expand...
Any idea what the weight and OAT were for these tests?
 
Doug,
Reality check time...

169.3 knots = 195 mph.
Van's posted cruise speed for a 180 HP RV-7A solo (from their web page): 198 mph.
Van's solo weight (posted, Hartzel 2 blade CS): 1,400 lbs.
Your solo weight (calculated from your original post): 1,550 lbs.

So even if the MT costs you 3-5 mph, and your extra solo weight costs you a couple more, you're still within 2% of "book numbers". Why do you think you're slow? Sounds more like you're "average" to me.
 
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Oat

Kevin,
My notes from 2 years ago suggest OAT 19 deg F @ 8000 feet. I don't have the OAT at 2000 so would have to use standard temp changes at alt to approximate. Weight would be approx 1140 + 230 + 120 for fuel (1/2 tanks as a guess only.)
 
Good question

Michael White said:
Doug,
Reality check time...

169.3 knots = 195 mph.
Van's posted cruise speed for a 180 HP RV-7A solo (from their web page): 198 mph.
Van's solo weight (posted, Hartzel 2 blade CS): 1,400 lbs.
Your solo weight (calculated from your original post): 1,550 lbs.

So even if the MT costs you 3-5 mph, and your extra solo weight costs you a couple more, you're still within 2% of "book numbers". Why do you think you're slow? Sounds more like you're "average" to me.
Click to expand...


Moose,
I appreciate the reality check question. That's one reason I hesitate to complain about a 195 mph plane... so I'm not complaining only trying to improve/tweak/etc. It's been 2 years and 300 hours so the tweaking bug has bit.

Vans top speed numbers as posted today on the web site for a 200hp, 2 blade prop, 1400 lbs is 215 mph. So I'm 195 mph best speed. 20 mph below stated top speed. I didn't post other numbers but at ~75% power I'm 165kts so 190 mph vs 205 mph from Vans for a 200 hp.

I'd like to pick up part of the 15-20 mph as I do use this plane for cross-country flights and quite honestly it's a pride thing as well.

Definitely not complaining but always tweaking/learning
 
Aileron Vertical Sidplacement

Hello Doug,
With people of the calibre of Kevin and Dan guiding us here, I hesitate to offer any suggestions, but I will relate a problem that I had.
I suspect you might have a couple of self cancelling rigging errors. My left aileron initially 'Floated' 1/2" up at cruise speed (and right one down... 'cause I remembered to connect them) producing a slight roll to the left (Left wing heavy) which increased with speed. Maybe you DO have a heavy left wing and something else is cancelling it.
Using a long straight edge on the lower side of the wing and across the aileron, I traced it to the right aileron sitting 1/16" lower than the left; even though they were QB wings and Ailerons, with pre-punched holes in the Chromoly aileron brackets. I could also measure the same difference in the distance between the top wing skin (at it?s rear edge) and the top of the aileron with a vernier depth gauge; in fact you could see it.

As recommended by Ken S at Vans, I removed the aileron brackets, slotted them to raise the right aileron 1/16" and did a flight test. Flew straight and level. Then drilled new brackets to the same dimensions.
I also think you should judge your aileron alignment in relationship the flaps, not the wing tips, which are notorious for twists ex-Vans.

If this all seems unlikely, disregard everything after Hello.
Cheer,
Pete.
 
Flaps are not always a good rigging reference.

Flaps can also be built with a twist in them so they should be checked before using them as a rigging reference.

The wing tips should never be used as a reference. In fact a properly rigged aileron positioned at neutral should be used for properly positioning the wing tip when installing it. A wing tip can be easily be installed with the T.E. 1/2 low or high relative to were it should be. This is often blamed on poorly made wing tips. Be sure it is properly aligned befor drilling any holes.
 
I was looking at you rate of climb figures and they don't look good up higher. Between 6500-7500 feet you averaged about 350 feet per minute climb. That is showing me that your engine is not developing the power it should. I think that would also be causing your speed problem.
 
7DeltaLima said:
I'd like to pick up part of the 15-20 mph as I do use this plane for cross-country flights and quite honestly it's a pride thing as well.

Definitely not complaining but always tweaking/learning
Click to expand...

Hi Doug

I've got a couple of thoughts, although most of the good suggestions have been made.

First, is it possible that your fuel distribution is way out of whack? Admittedly this is unlikely if your engine is smooth, but it's possible that you're not getting all the cylinders at best power simultaneously, which could cost some power. Don Rivera at Airflow Performance might have some input here.

Second, the influence of gear and especially gear leg fairings is significant. Is it possible to jack your airplane on the ramp (on a calm day!) to get the weight off the gear? This would allow you to back off and look at the fairings to see if they are well aligned in the direction of flight.

It might also be worthwhile to check your engine's thrustline. You can do this by putting a digital level on the crankcase seam, and comparing it to the longerons. If your engine mounts are especially saggy, it might be that your thrustline is too low, effectively making your airplane seem heavier and slower.

James Freeman
 
7DeltaLima said:
Kevin,
My notes from 2 years ago suggest OAT 19 deg F @ 8000 feet. I don't have the OAT at 2000 so would have to use standard temp changes at alt to approximate. Weight would be approx 1140 + 230 + 120 for fuel (1/2 tanks as a guess only.)
Click to expand...
The rate of climb comes out to about 1,945 ft/mn, at an average altitude of 3,500 ft. Based on Van's claimed performance, at 1500 lb weight, I would expect about 2,400 ft/mn at sea level std day, with a Hartzell prop. The power at 3,500 ft will be a bit less than 90% of the sea level power, so the rate of climb you got is in the expected ball park, I think. That suggests that the engine isn't grossly down on power, I think. It certainly isn't down on power enough to explain the speed shortfall.

If you measure the wing incidence at various spanwise locations on each wing, how much variation is there?

Do you have any mods that affect the exterior of the aircraft, in any way?

What method did you use to set the rigging of the flap and ailerons? Airfoil templates? Lining up tooling holes? Something else?
 
Bryan Wood said:
Just curious Dan, how much speed did you pick up by keeping the vents closed when you tested?
Click to expand...
I picked up just shy of 2 knots, but the tests were done on different days in slightly different conditions. Could be (and probably is) a wash. It's just the principle of having the vents closed to reduce drag that I'm yappin about here.
 
fodrv7 said:
Hello Doug,
Maybe you DO have a heavy left wing and something else is cancelling it.
Using a long straight edge on the lower side of the wing and across the aileron, I traced it to the right aileron sitting 1/16" lower than the left; even though they were QB wings and Ailerons, with pre-punched holes in the Chromoly aileron brackets. I could also measure the same difference in the distance between the top wing skin (at it?s rear edge) and the top of the aileron with a vernier depth gauge; in fact you could see it.
Click to expand...
Pete, thanks for the thoughts. I've looked at the aileron distance vs top skin and I can't find any difference. After I saw this on Dan's site I thought it might be the reason the left aileron appears lower than wing tip but I could not find a measureable difference. I'll look at it from the bottom. Didn't really look at it from that standpoint.

There's one symptom that seems to be common that you and Dan reported that I'm not really seeing.... airspeed doesn't seem to effect the relationship between the aileron and wing tip.
 
Kevin HortonThe rate of climb comes out to about 1,945 ft/mn, at an average altitude of 3,500 ft. Based on Van's claimed performance, at 1500 lb weight, I would expect about 2,400 ft/mn at sea level std day, with a Hartzell prop. The power at 3,500 ft will be a bit less than 90% of the sea level power, so the rate of climb you got is in the expected ball park, I think. That suggests that the engine isn't grossly down on power, I think. It certainly isn't down on power enough to explain the speed shortfall.
Click to expand...

Remember these numbers were with about 12 hours on the engine, no wheel pants and only fairings on the main, nothing on the nose.

If you measure the wing incidence at various spanwise locations on each wing, how much variation is there?
Click to expand...
I'll reverify but when looking to see if the ailerons were maybe off in relationship to the wing skins I did throw the digital level on the wings in a few spots and don't remember anything jumping out as being "screwy".

Do you have any mods that affect the exterior of the aircraft, in any way?
Click to expand...
No mods, not smart enough to do anything but follow directions. :)

What method did you use to set the rigging of the flap and ailerons? Airfoil templates? Lining up tooling holes? Something else?
Click to expand...

Tooling holes. You'd think that'd be hard to screw up :)
 
flyeyes said:
Hi Doug

I've got a couple of thoughts, although most of the good suggestions have been made.

First, is it possible that your fuel distribution is way out of whack? Admittedly this is unlikely if your engine is smooth, but it's possible that you're not getting all the cylinders at best power simultaneously, which could cost some power. Don Rivera at Airflow Performance might have some input here.

Second, the influence of gear and especially gear leg fairings is significant. Is it possible to jack your airplane on the ramp (on a calm day!) to get the weight off the gear? This would allow you to back off and look at the fairings to see if they are well aligned in the direction of flight.

James Freeman
Click to expand...

James, this engine really sounds and feels smooth. It feels good on takeoff. Sits you back like you'd expect. I believe the engine is putting out full power.

Which makes your second point even more interesting. I was even thinking about pulling the fairings off, go flying and seeing how the wings balanced without fairings. Think I'll follow your suggestion first to see if anything jumps out.
 
Luebben said:
I was looking at you rate of climb figures and they don't look good up higher. Between 6500-7500 feet you averaged about 350 feet per minute climb. That is showing me that your engine is not developing the power it should. I think that would also be causing your speed problem.
Click to expand...
You've misinterpreted the way that the climb data was presented. The stop watch was started at the bottom of the climb, and it ran continuously. The time at each thousand feet in the climb was recorded. So, the time of 2:56 represents the time between 2,500 and 7,500 ft, not the time between 6,500 and 7,500 ft.
 
Steps taken

Group:

Here's what I've done in the last week or so trying to find root cause and/or answers to some of the other questions/suggestions.

1) Checked Aileron alignment... Pulled the wing tips off and verified tooling holes lined up. With the right aileron locked in position the left aileron was a "little" low. I raised the left aileron maybe 3-4 half turns on the push rod. Now it is dead center.

2) Jacked the plane up and remeasured the wheel pant positioning . Everything lined up and I don't think I could improve it. (really thought this might be the issue)

3) Manifold pressure is >28 on takeoff. RPM 2700. I can't find anything that would hint that the engine isn't making full power.

4) The counter weight on the rudder is aligned with the HS in flight.
5) I did glass the inlet ducts pass thru on the cowl on original build.

Results, no diifference. Orignal was 169.3 top speed. Last run, at 8k den alt I saw 170.7 with a .7 std dev.

The left aileron is still floating down and the right up (as Peter said "'cause I remembered to connect them" :) ) . Sitting on the ground, ailerons do line up with the wing tips (verified aileron alignment via tooling holes) but after take off and leveling off, the left aileron is down maybe 3/8-1/2 inch. This has to be attributable to some aileron bracket mis-alignment (as suggested by Peter and Dan) but I can't prove it by measurement yet. That will be my next focus.

Follow up questions:

1) Any more ideas that I should check?
and
2) Anyone else running the MT 3 blade prop? This is the only major "planned" difference in my ship versus Van's stock plan I do not want to insinuate that the prop is cutting 10 knots off the top end when it could be something that I have improperly rigged BUT if anyone else is seeing the same thing then I can quit chasing a ghost. I have read all the other posts about the MT 3 blade and have seen Van's test numbers. I'm looking for contact with any other builder flying behind a MT 3 blade prop that is willing to share performance numbers either directly with me or via a public post. (not willing to invest $6k to test with another prop :)

Thanks in advance.
 
7DeltaLima said:
2) Jacked the plane up and remeasured the wheel pant positioning . Everything lined up and I don't think I could improve it. (really thought this might be the issue)
Click to expand...
How about gear leg fairing alignment?
 
7DeltaLima
It sounds like you have covered the bases pretty well. I,m flying a 7A that I built and it is a little slow but i true out at 177 kts. I'm guessing it is the prop.
 
Which MT blade?

What blade model does your MT prop have? I've got efficiency charts for the 175-59 blade, and the previous Hartzell prop (not the blended airfoil one), and I would be interested in seeing what efficiency MT claims at your test conditions, compared to what Hartzell claims.
 
Prop

Kevin Horton said:
What blade model does your MT prop have? I've got efficiency charts for the 175-59 blade, and the previous Hartzell prop (not the blended airfoil one), and I would be interested in seeing what efficiency MT claims at your test conditions, compared to what Hartzell claims.
Click to expand...

Prop > MTV-12-B/183-59
 
7DeltaLima said:
Prop > MTV-12-B/183-59
Click to expand...
Just to be 100% sure, before I send an e-mail to MT to request some data - there is no "B" at the end? I.e. 183-59B?

The B, if present, indicates a different twist on the blade. It is interesting that Van sells the MTV-12-B/183-59B. I have to assume that they choose the best twist available. If you have a 183-59 (no B), then having the less than optimum twist could reduce the performance. Maybe.
 
Kevin Horton said:
Just to be 100% sure, before I send an e-mail to MT to request some data - there is no "B" at the end? I.e. 183-59B?

The B, if present, indicates a different twist on the blade. It is interesting that Van sells the MTV-12-B/183-59B. I have to assume that they choose the best twist available. If you have a 183-59 (no B), then having the less than optimum twist could reduce the performance. Maybe.
Click to expand...

Kevin,
Interesting catch. There is no "B" at the end. The JAA Form One is dated to Vans on 05-16-2001. I didn't buy it directly from Vans. I bought the engine (Aerosport) and prop new in the box from an individual in TX who had changed his mind about completeing an 8. He had purchased the prop from Vans. The part number as listed on both the JAA Form One and the prop log book is MTV-12-B/183-59. Hub Serial # 01154 mfg 2001. Low pitch 10 deg +- 0.2 and high pitch 35 d +- 1.

It would be interesting to know if Vans/MT decided to change the pitch for increased performance.



Doug
 
7DeltaLima said:
Kevin,
Interesting catch. There is no "B" at the end. The JAA Form One is dated to Vans on 05-16-2001. I didn't buy it directly from Vans. I bought the engine (Aerosport) and prop new in the box from an individual in TX who had changed his mind about completeing an 8. He had purchased the prop from Vans. The part number as listed on both the JAA Form One and the prop log book is MTV-12-B/183-59. Hub Serial # 01154 mfg 2001. Low pitch 10 deg +- 0.2 and high pitch 35 d +- 1.

It would be interesting to know if Vans/MT decided to change the pitch for increased performance.



Doug
Click to expand...

Thought I'd post what I'd found concerning the "b" designation on the MT 3 blade prop.

Van's support groups response ...
If MT changed the prop, it wasn't at our instigation. We just ask them to supply the ones they think will work best on RVs. We don't do any scientific testing to assess their performance. That said, the limited tests we have done seem to indicate that the HArtzell is a little more efficient.

We don't know exactly what the extra b (should be lower case) on the end of the prop blade number means, you'd have to ask MT. It does indicate a change in blade twist; presumably they thought it would be better than the non b version for RVs, but whether it actually makes any difference, we don't know.

Vans

MT's response via Jim Ayers at Less Drag Products....
The new 183-59b blades remove the mid range RPM restriction on your Lycoming 360 engine, and increase your cruise speed by about 5 mph.

Jim Ayers
Less Drag Products, Inc.
(805) 499-8646 FAX


So... I'm considering swapping out the blades but not certain yet. I don't believe the RPM restriction would apply to me as the A1B6 has weighted crank. Performance testing is such a subjective thing as well. It is so difficult to do accurate performance tests to prove/disprove a 5 mph gain. In either case, the "b" is the new blade with a different twist that MT sells via Vans and it doesn't have RPM restriction for 360 engines.

Doug
 
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