aerobatic engine

[Bob Greenall greenall@ptd]

I am looking to purchase a run out or mid time engine for my 7.In order to do aerobatics does the crank need to be a certain type.Solid flange etc.

[Crossbow]

Originally Posted by Bob Greenall greenall@ptd

I am looking to purchase a run out or mid time engine for my 7.In order to do aerobatics does the crank need to be a certain type.Solid flange etc.

While I am still a good way from getting my engine (I just finished my fuel tanks), however I have researched the issue a bit, so here are my thoughts.

I think that what you might be looking for is a fuel injected engine with an inverted oil system.

Also, you can either use a fixed pitch prop (solid crankshaft or plugged hollow crankshaft), or a constant speed prop (which would have a hollow shaft). Either one will work, although the constant speed prop would be better if you can deal with the added weight, complexities, and costs.

However, do avoid using electric constant speed props and prop extentions for acrobatic use.

And fuel injected engines tend to work better in acrobatics, but are not they are certiantly not required. However, with fuel injection you will have to deal with the increased complexity and cost of such a system.

I hope this helps!

[Bob Greenall greenall@ptd]

Thank you for your quick response.I am familiar with the oil,fuel and conatant speed prop systems.Some of the prop mounting flanges on the crank I believe are either solid or have lightning holes in them.

[sandifer]

A solid flange is ideal, but unless you plan on doing snaps and gyroscopics, you should be fine with a lightened flange for RV style acro. AD 84-13-05 was issued for "AEIO" Lycomings with the original lightened flange that requires a flange inspection every 25 hrs. Not applicable to non "A" aerobatic engines.

[Vern]

Most RV'ers do not do hard acro, but tend to do an occasional aileron roll or loop. These are NOT Pitt's Specials.

Therefore, unless you are really going into strenuous acro, most any engine-prop combo will do just fine (not electric props). Likewise, carbs and standard fuel pickups are just fine for the occasional loop, roll, immelman, split -s, barrel roll, or spin.

New builders/dreamers often spend too much money and time and end up with over-kill on their projects. Just build according to plans, get in the air as soon and cheap as possible. Then, as you gain experience, you will fine tune your dream.

[jrs14855]

There are three basic configurations on cranks related to aerobatic use:
Solid shaft in front main bearing area, not useable for oil controlled constant speed. Contrary to popular belief these were not developed for aerobatic use but were for the Cherokee 180 around 1965. They are used on many S1 Pitts and similar aircraft. Some of the later manufacture aerobatic shafts had thicker flange.
Hollow shaft for oil controlled constant speed. May be standard flange thickness or heavy flange. No lightening holes
Lightening hole flange shafts. These are real antiques. Typically early 60's Cherokees, Tri Pacer, Apache etc. I personally would not use a lightening hole shaft with a metal blade prop, either fixed pitch or Constant speed. There is very little difference in pricing considering either a certified shaft with/without lightening holes or an engine with/without lightening holes. Another consideration is that many of the engines with lightening hole flanges are conical mount engines. Fine with a wood or MT etc prop but they tend to transmit a lot of vibration with metal fixed pitch or constant speed.

[Danny7]

what happens with electric props and aerobatics?

showing how little i know here, that's ok

[jrs14855]

If the electric prop is an MT with the wood composite blades, the load on the crank would be similar to the wood/composite blade oil controlled MT props. The lightweight blades, whether carbon fiber or wood composite subject the crank to only a small portion of the loads imposed by heavier blades. I have no knowledge as to whether the electric MT is suitable for aerobatics.

[Crossbow]

Originally Posted by Danny7

what happens with electric props and aerobatics?

showing how little i know here, that's ok

Sorry, but I do not know the details as to what happens if you use an electric prop and aerobatics, however if you look at the electric MT propellers in the Vans catalog, it does state that:

... Electric props are NOT recommended for aerobatics.

And while it is true that it is a recommendation as opposed to a prohibition, however if the manufacturer states such a thing, in my opinion it is wise to follow their advice.

[4kilo]

Typically electric propellers do not respond to changing pitch requirements as quickly as hydraulic (oil) controlled propellers. This means that during aerobatic manuevering, the electric prop will probably not be able to maintian a constant RPM - it just can't react quickly enough. It's quick enough for normal flight, just not acro.

Pat